Glossary of Terms

Ethernet network twisted pair at up to 1000 Mbps

Ethernet network twisted pair at up to 100 Mbps

Ethernet network twisted pair at up to 10 Mbps

A Half duplex RS-485 connection system which uses one twisted pair for Data A(-) and Data B(+), plus Signal Ground/Common.

Transmit and receive operations are on the same pair of wires, allowing all devices on the bus to communicate with each other. The system requires that each slave have a turn-around delay of one or more characters between receiving data and responding. Each device must be separately addressable, and ignore data/commands that don't apply to the device’s address. All 2-wire RS-485 devices are normally in receive mode except when transmitting. Receivers can either be disabled when the device is transmitting, preventing an echo of the sent characters from being received on the sending device (Echo off). Alternately, the sending device may leave its receiver enabled to detect any collisions from other devices on the bus (Echo on). Driver/Receiver control can either be implemented through software in the node or through hardware. B&B converters and serial cards offer this option through either the RS-232 RTS line for software control or Automatic Send Data (SD) control in hardware.

3 meters is about 9.8 feet. See meter for conversions.

A RS-485 transmitter must be Enabled to transmit or Disabled when not transmitting. When Disabled, the transmitter is set to a high impedance state (tri-stated). The 485 Driver must be controlled unless set to "Always" Enabled for RS-422 operation.

Depending on the device circuitry and model, the driver control may be "RTS" controlled or "SD" (Automatic Send Data) controlled.

RTS controlled drivers require special software to raise and lower the RTS line on the RS-232 port for each transmission. RTS control is not usually suitable for Windows systems because RTS timing cannot be closely controlled, then data is lost.

In SD mode, additional circuitry controls the transmitter. Some models have a preset fixed R/C timing circuit preset for 9600, or switch selectable presets, or bit-wise enable timing. Serial cards may use bit counters or the UART Transmit buffer status line for control.

In Half Duplex operation, the 485 Driver Control signal is also used to Disable Receive during Transmit, and Enable it at the end of Transmit.

2-wire RS-485 system is Half Duplex using one twisted wire pair plus Signal Ground/Common. The wire pair is used alternately for either transmit or receive by the master or slaves.

4-wire RS-485 system is Full Duplex using two twisted wire pairs plus Signal Ground/Common. One pair is used for transmit from master(s) to slaves, the second pair for the slaves to transmit back to the receiver on the master(s). Software flow control can be used since both Transmit and Receive are active at once.

A Full duplex system which uses one twisted pair (TDA & TDB) for transmitting, a second twisted pair (RDA & RDB) for receiving, plus a Signal Ground/Common.

In a RS-422 system, there are normally two units (master/master or master/slave), or one master with multiple listeners which don't transmit back.

In a 4-wire RS-485 system, there can be one or more masters, talking to multiple slaves. Each slave must be addressable and have RS-485 transmitter enable (as in 2-wire). A single master multi-slave system is sometimes called "half-422" because the master is set for RS-422 operation, but the slaves must be set for 485 transmit.

Analog-to-Digital conversion. The conversion of an analog voltage into one of many digital steps that corresponds to the voltage. The digital value represents the voltage at the time it was sampled. The number of bits determines the number of steps within the full analog range and how fine the resolution is.

1. One of the Centronics parallel port interface handshaking lines used to by a printer to acknowledge that the data byte sent was received and processed. Used by some printers to acknowledge that return data is ready for transfer to the host (Bi-directional Printers). Used by the host together with the Busy handshaking line so that data is not sent until the end of Busy and Acknowledge. (Printer context)
2. A device dependent string that indicates back to the host that the command was received and is a valid command, not a unsupported command or invalid command for the current operating mode. Not-acknowledge (NACK) is often returned when invalid commands are received. (Serial device context:)

Current Loop - When one side of the current loop is active, it supplies the current for the passive side. There is usually a transmit loop and receive loop on any one device. Either or both can be active. Current flows during a "MARK," “IDLE,” or “1” state. During a "SPACE," “START,” or “0” state, no current is supplied. Refer to our Current Loop Application Note for more info.

1. A Windows PC has I/O port addresses and Memory addresses. Some devices use both types of addresses. I/O port addresses have a 64K address space, devices may decode all 16 address bits or only some of the lower bits. Address setting in our ISA bus serial cards is by DIP switches (selecting bits 11-4), (Jumpers for Com 1-4 on 422ICCA) or on our PCI cards, by the Plug 'n' Play OS or under NT 4.0, by the drivers. (computer address context)
2. Depending on the RS-485 device, the device address can be set by DIP switches or by software command and saved in non-volatile memory. This allows multiple units to be connected to the same multi-drop network.(RS-485 device context)
3. Depending on the model, addressing may be fixed or stored by a setup program in non-volatile memory. (Smart Switch context)

A device that responds to only to a unique character or bit sequence. Usually shares a network or serial port with other devices or ports. In a RS-485 network, one byte in the control sequence is the address byte (0-255). In a Smart Switch, one byte in the command sequence selects the port. Some devices (such as slot machines) use a multi-byte encoded serial number for addressing.

A operating mode on B&B Electronics Fallback Switch (see model 232FBC) - Connects to the primary serial device. At any time the alternate device asserts itself it is enabled and the Primary port disconnects.

Analog current loops are used to transfer analog values from temperature or relative level sensors over long distances. Currents typically range from 4-20mA for relative value. Analog current loop values can be converted to digital values representing the current or relative value using an A/D converter after converting the current to a voltage.

Digital current loops differ from analog current loops and are used to send/receive digital signals, with the presence and absence of current used to designate a “1” or “0” state respectively.

The active state of a control line. In RS-232, the DTR, DSR, CTS and RTS lines are held high when the line is asserted.

Form of serial communication used on personal computer RS-232 ports, RS-485 and most RS-422 communications. No separate synchronizing clock signal needs to be transmitted for the data. This Non-synchronous serial communications format uses standard preset baud rates based on a crystal reference for transmit timing, and uses the received data Start Bit and a local crystal reference to read the remaining bits near the center position. Compare to Synchronous Transmission which requires two synchronizing signals, receive clock and transmit clock plus two data signals.

The Auto Select mode allows the 232BSS4 slave ports to initiate communications with the Smart Switch. Master port. The presence of data on the slave port will automatically connect it to the host on the master port. The other ports will buffer data until it is their turn to connect to the host. The set up allows the user to establish how long the master will stay connected to each port. The host has the ability to reply to the slaves and override the automatic switching by selecting a specific port.

Circuitry found on many of B&B’s RS-485 products which sense the presence of RS-485 data to be transmitted and sets the RS-485 transmitter line driver ON to send the data. At the end of transmission, it returns the line driver to a high impedance (disconnected) state. Can also disable the receiver (for Echo Off) during transmit, enable it again at the end of transmission.

A device or RS-485 driver/receiver unit which cannot be communicated with. A bad node can be caused by defective wiring or a loss of power (when devices are not tri-stated during power off), or by failure in one device that blocks the data to all the others.

Devices used to read bar codes into a computer. Used at Point-of-Sale (POS) checkout counters, for pricing, inventory control, parts tracking, routing or shipping documents. Could also be magnetically identify ID and authorization for entry by other means for security gates and facility entrance or elevator floor access.

The data rate in bits per second (bps) on a serial communications port. For 8 bit data with one start bit and one stop bit, the bytes per second is the baud rate divided by 10. At 9600 baud, and 10 bits per character, the character rate is 960 bytes per second (Bps).

A serial device that receives data at one baud rate from one port and transmits it at a different baud rate at another port. A duplex converter provides conversion in both directions. A well designed converter will include input/output buffering and provide flow control so that no data is lost converting to the slower port. Used to convert newer (higher baud rate) equipment for use with older (lower baud rate) systems, or to allow newer systems to access older equipment. See 232BRC & 232BSS4 Smart Switch.

A twist locking Coax type connector used on 50 or 75 ohm Coax - used for RF & older style network connections

bits per second - data rate in bits, commonly referred to as baud rate

Bytes per second - data rate in bytes (8 bits)

1. Memory that holds data until it can be used, sent or processed. (Computer data context)
2. Active circuitry that performs circuit impedance matching, isolation, amplification, raises the input impedance, lowers the output impedance or increases the current drive capabilities or voltage handling capabilities. (Electronic circuit context)

Circuitry which provides electronic circuit buffering for digital inputs/outputs or analog inputs or outputs. See also Signal Conditioners & Isolators

An electronically controlled serial data switch that includes buffer memory for input and output ports. A serial data controlled switch is a switch that can select one of several ports for connection to the master port. The switch watches the incoming data stream for a sequence of characters it recognizes as the command. It then changes the master connection as indicated by the command.

Electrical interconnections in common with other circuits or devices. A power bus provides a common source of power connections, a ground bus, common ground connections for power and/or signal common. A RS-485 bus is the network of wiring joining various 485 devices together.

A computer bus provides for internal expansion cards, one of the first commonly used busses was the S-100 bus used on CPM machines. The original IBM personal computer has an 8-bit data bus, the original AT has a 16-bit data bus. These were copied for compatibility by other computer companies. The PC bus and PC-AT bus interface is now called ISA for Industry Standard Architecture. There are other common busses, including PCI and a variety of industrial busses.

When you want to expand your serial ports or add other functions using a internal card, you need to know what type of expansion bus the computer has. Check the specifications, verify that the desired bus slot is unused. PCI bus or ISA slots are common in desktops, PCMCIA slots on laptops, USB (Universal Serial Bus) connectors may be available for external expansion on desktops or laptops.

1. In a parallel printer interface, the Busy status line is set by the printer when it is processing a character. Busy is cleared when the printer is finished processing the character. When the printer is not Busy and not in Acknowledge state, the Strobe line can be set inactive and the next character can be placed on the printer data lines. Next the Strobe is set active to command the printer to read the next character, and the printer sets Busy again. Busy is used with the printer Acknowledge line for character by character handshaking.
2. In a serial device with handshaking, the CTS line indicates Busy by being set low. When able to receive another character, CTS goes high. Some serial devices will return a Busy character sequence when in the middle of another task, other devices simply don't read or respond to any input when busy. Devices with software handshaking may send a X-Off sequence to indicate Busy, then send X-On when able to receive again.

Centronics type 36 pin male printer connector used on cable. Uses bail lock retainer on the printer connector to secure the cable connector. The Centronics parallel standard uses 36 pin connectors.

Centronics style 50 pin connector used for original SCSI

Controller Area Network. The CAN protocol is an ISO standard (ISO 11898) for serial data communication. Originally developed for automotive applications, CAN has gained widespread use in industrial automation and mobile machines as well.

The CAN standard includes a physical layer and a data-link layer which defines a few different message types, arbitration rules for bus access, and methods for fault detection and fault confinement. The physical layer typically uses differential transmission on a twisted pair wire.

In fiber optic converters manufactured by B&B Electronics, the carrier is unmodulated light. The signal is transferred by turning the light off and on. In the 25PFLST & 9PFLST units the RTS & TD the two signals are sampled alternately at high speed to multiplex then together. Other types of devices may use light turned off and on at some frequency such as 38KHz, then pulse code the carrier.

1. In RS-232 ports and devices, the CD is the Carrier Detect line from a modem (also called Data Carrier Detect, or DCD). When a modem answers the phone, it looks for the modem carrier, then sets the CD line active when the carrier is present. The computer monitors that line to know when to try connecting or when to hang up if the carrier is lost.
2. Compact Disc - A computer CD is usually a CD-ROM disc with data such as Installation software, documentation. Contents vary, but the discs are read-only to most drives.
3. Compare to DVD which is a higher density version of the CD.

The CE mark indicates compliance with the regulatory requirements of the European Union. All of our products meet the requirements of the US FCC. Those with the CE mark have gone through the additional susceptibility tests required under the European EMC directive.

1. In serial communications a channel is a path for communication. One path is usually transmit, another is receive. Receive and Transmit are two channels. RS-232 can have several other channels, the handshaking CTS and RTS channels, the DSR and DTR channels, the CD and RI channels. In a multi channel RS-422 converter, each channel uses one twisted pair of wires, and all channels share a common signal ground wire.
2. A path of communication or access point for software connection.
3. A range of radio frequencies used by a transmitter/receiver during communication or broadcasting or reception. Each channel can be set or preset.

BNC (twist lock) for network, F59 (screw on) for Television/VCR Coax/cable input
BNC Connector on side of pH device

A switch that selects a connection or disconnection according to a multiple byte/character command sequence sent to the master port. Sequences sent from the slave ports are ignored by the master. Some code activated switches are selected by setting combinations of the DTR and RTS RS-232 lines to select command mode, then the command data is read in by toggling the lines.

Commonly found connectors for computer and data interfaces are typically labeled M for male/plug or F for female/socket/jack/receptacle. Following is a partial list of common connectors.

C36 - Centronics type 36 pin connector used for printers

DB9 - 9 pin "D" connector

DB25 - 25 pin "D" connector –

Female

Mini phone (3.5mm sleeve) Sub mini phone (2.5mm sleeve)

Screw terminals
See the screw terminals at the ends of the surge protector

ST Connector – popular type of fiber optic connector

RJ-11/RJ-12 - RJ-11 is 4 contact modular phone plug/jack RJ-12 is 6 contact

RJ-45 8 contact large modular network type plug/jack

Terminal Blocks – sets of screw down contacts for making direct wire connections

USB-A (USB type A connector male plug/female receptacle) Downstream
   

USB-B (USB type B connector male plug/female receptacle ) Upstream
   

DB9 Female

DB9 Male

DB25 Female

DB25 Male

DB37 Female

RJ-11 Female

RJ-12 Female

RJ-45 Female

Terminal Blocks

Terminal Board (same as terminal blocks)

A device that converts electrical signals from one format into another. Conversions are electrical, electrical to light (for fiber optical cable), Infrared light or RF.

A RS-232 to RS-422 Converter changes 2 or more channels of single-ended RS-232 signals to balanced differential signals. Single-ended RS-232 lines may range from -12 to -3 volts (referenced to signal ground/common) for the mark/deasserted state to +3 to +12 volts for the space/asserted state. RS-422 differential signal pairs have two outputs 180 degrees out of phase. When the data B (+) line is +5 volts and the data A (-) line is low (0 volts) (MARK condition) or opposite (SPACE) with the data B line low and the data A line +5 volts. A pair of RS-422 converters can be used to extend RS-232, one converter at each end.

B&B Converters have a transmit path and receive path, some RS-485 Converters are Half Duplex 2-wire mode and either transmit or receive at one time, while others are Full Duplex 4-wire mode, able to transmit and receive at the same time.

Standard RS-232 to RS-485 converters are not addressable from the RS-485 side, all signals received on the RS-485 bus are converted to RS-232 receive signals, and all RS-232 transmit signals are converted to RS-485 transmit signals. One RS-485 to RS-232 Distributed Smart Switch/converter (485DSS) is addressable from the RS-485 side, it permits a RS-232 device to be connected as a slave on a 4-wire RS-485 network. This device cannot function as a RS-232 to RS-485 master since conversion is only available after activation from the RS-485 network side.

1. Central Processing Unit - The primary computing unit in a mainframe computer.
2. The main microprocessor in a computer or device - in the PC today, this is usually a Intel Pentium class processor or competing AMD or Cyrix microprocessor. In separate device with a microprocessor, the microprocessor is the CPU for the device. If a device has a microprocessor, it is said to be a "Smart" device, without a microprocessor, it is a "dumb" device.

Clear To Send - the handshaking line asserted by a DCE device to indicate to a DTE device that it can accept data. The DTE device sets the RTS line, the DCE reads the RTS line to know if the other device can accept data.

1. Digital Current loop is a old method of making relatively long distance serial connections. It can be converted to RS-232 or RS-485. Current loop connections date back to Teletype machines and 75bps or slower data rates. Typical current loops use 20mA current to indicate an “IDLE,” "MARK," or “1” condition and 0 mA to indicate a “START,” "SPACE," or “0”. Current loop connections can have high noise immunity and built-in ground loop isolation, but the speed is usually limited to 19.2kbps data rates or less. Current loop systems are less standard than other formats (RS-232/422/485) since receivers or transmitters may be either passive or active and some may use other current values. Current loop is seldom used in newly designed installations.
2. Analog current loops are used to transfer analog values from temperature or relative level sensors over long distances. Currents typically range from 4-20mA for relative value. Analog current loop values can be converted to digital values representing the current or relative value using a A/D converter after converting the current to a voltage.

Digital to Analog converter - a D/A accepts a digital value and converts it to an analog voltage for output. The bits of conversion determine the steps of voltage resolution.

The A data line in a half duplex 2-wire RS-485 system. The EIA RS-485 standard defines the line as Low in the MARK state, when the B line is high. Some manufacturers label Data A as Data(-). In an RS-485 two wire network, Data A is a combination of Transmit Data A and Receive Data A lines.

Data Collection. Computer data acquisition requires sensing external conditions such as switch closures, temperature, cycles, proximity, weight, size, color, markings, Infrared images, light, and such using A/D (voltage) converters and Digital Inputs.

Computer data acquisition is usually for control purposes, the conditions are sensed to control things that affect the conditions, turn on a pump when the levels get low, turn off when at the upper level, remotely read flow rates, pH, control processes that require constant adjustments.

Output control signals can be voltages, or digital, turning things on/off.

The B data line in a half duplex 2-wire RS-485 system. The EIA RS-485 standard defines the B line as Positive in the MARK state. Some manufacturers label Data B as Data(+). In an RS-485 two wire network, Data B is a combination of Transmit Data B and Receive Data B lines.

Isolation between the signal line input and output, and between the signal line common/ground on the input side and output side. Isolation is rated in volts of isolation between all inputs/outputs and signal grounds/commons on one side compared to the other. Isolation requires separate power supplies or magnetically (switching supplies) between one side and the other.

In serial data, the RS-232 Receive & Transmit lines, or the RS-422/485 TD(A), TD(B) and RD(A), RD(B) lines, or in a 2-wire RS-485, Data A and Data B.

The data lines require a signal ground/common for reference to the signals. Even differential data lines should be provided with a reference common wire connection.

In a parallel printer, Data lines D7-D0.

Supported baud rates in bps (bits per second) or transfer rates for other devices.

15 pin "D" connector – sometimes used for video as well as some PLC communication ports

25 pin "D" type connector - (looks like a sideways D) The top row has 13 pins (or holes for pins), the bottom has row has 12 pins (or holes for pins). If the connector has pins, it is Male (DB25M), if it has holes to accept pins, it is Female (DB25F).

Male

Female

37 pin "D" type connector - (looks like a sideways D) - similar to DB9 and DB25 except more pins/receptacles.

37 pin "D" connector - same as DB25 type except more pins

9 pin "D" type connector - (looks like a sideways D) The top row has 5 pins (or holes for pins), the bottom has row has 4 pins (or holes for pins). If the connector has pins, it is Male (DB9M), if it has holes to accept pins, it is Female (DB9F).

Male

Female

A DB type 9 pin plug connector, another name for a DB9M (male) connector.

A DB type 9 pin socket connector, another name for a DB9F (female) connector.

Data Communications Equipment - (such as a modem)

The RS-232 DTE or DCE designation determines whether a signal is a input or a output. A DTE device outputs a Transmit signal to the Transmit input on a DCE device. Although designations are the same, the functions of the signals are reversed between DTE and DCE.

RS-232 DTE/DCE Cables - Illustration List

Physical signaling method by which a pair of wires is used to transmit a signal. The differential transmitter (+) and (-) outputs are 180 degrees out of phase with each other (when one is +5V, the other is 0 volts, and when the first is 0 volts, the second is +5V). The receiver uses the difference between the two lines to determine the digital state. With differential signals, any induced common mode signals picked up on the twisted pair wires are cancelled at the receiver since it sees only the difference signals. Differential signals and common mode rejection help provide reliable serial communication over larger distances than single ended communications.

Digital Current loop is a old method of making relatively long distance serial connections. It can be converted to RS-232 or RS-485. Current loop connections date back to Teletype machines and 75bps or slower data rates. 20mA current loop indicates that it uses 20mA current to indicate an “IDLE,” "MARK," or “1” condition and 0 mA to indicate a “START,” "SPACE," or “0”. Current loop connections can have high noise immunity and built-in ground loop isolation, but the speed is usually limited to 19.2kbps data rates or less. Current loop systems are less standard than other formats (RS-232/422/485) since receivers or transmitters may be either passive or active and some may use other current values. Current loop is seldom used in newly designed installations.

Analog current loops differ from digital current loops, and are used to transfer analog values from temperature or relative level sensors over long distances. Currents typically range from 4-20mA for relative value. Analog current loop values can be converted to digital values representing the current or relative value using a A/D converter after converting the current to a voltage.

Digital Input/Output – A digital signal can be in only one of two states. A digital input would detect which of these states the signal was in. Some examples would be a switch open/closed, voltage present/absent, or a signal above/below a specific trip point.

A Digital output means setting a signal to one of two states. Some examples would be providing drive current or absence of current for another circuit, setting indicators on/off, turning relays on/off. One digital output can be either high or low, a combination of digital outputs can be used to obtain several levels of output.

circular connectors with various pin numbers and layouts, varieties used for PC keyboard connectors.

A standard metric sized mounting rail for use in a equipment rack or cabinet. Product housings/packages designed to attach to standard sized DIN rails. B&B stocks 35mm DIN rail with 7.5mm depth & 15mm depth

DIN Rail Package

1. In a 2-wire RS-485 system, the transmit driver must be enabled to transmit and disabled to receive.
   
   RTS (control)
   Converters and serial cards with RTS control use the RS-232 side control line Request to Send (RTS) to enable and disable the 485 driver. This requires the application software to raise the RTS line before transmitting, then lower RTS after the transmission is complete.
   
   SD (Control)
   Converters and serial cards with SD (Send Data) control include timing circuitry that automatically enables the RS-485 Transmit Line Driver when data is to be transmitted. The circuitry disables the driver within one character length after the transmission is complete. This type of RS-485 driver control has no special software requirements.
2. Software driver control uses software to control certain operating parameters of a hardware device. For example, a printer driver controls the printing direction, and printing methods.

1. Software drivers provide a standard software interface for a computer Operating System such as Windows, MacOS, UNIX, Linux, SunOS or Solaris.
2. Hardware drivers provide current or voltages to other hardware devices. The line driver in a RS-485 system is a transmitter that provides voltage and current drive to the receiving devices on the RS-485 network.

Data Set Ready - A RS-232 serial port line which is held high (+3 volts or more) when the data set (DCE device) is turned on and available. This is one of the handshaking lines. A device wanting to communicate with the device (or modem) may check the status of this line to determine if the device is available.

Data Terminal Equipment - (such as a computer or serial terminal, PLC or RS-232 Printer)

The RS-232 DTE or DCE designation determines whether a signal is a input or a output. A DTE device outputs a Transmit signal to the Transmit input on a DCE device. Although designations are the same, the functions of the signals are reversed between DTE and DCE.

RS-232 DTE/DCE Cables - Illustration List

Dual Tone Multi-Frequency (also known as Touch Tones) - two tones of a set of 8 tones are generated by a DTMF keypad. Each row (1, 4, 7, star) activates one tone, each column (1, 2, 3, A) activates a second tone. The standard telephone keypad omits column A (A, B, C, D). DTMF tones can be carried by voice links, and they are generated by most telephones and telephone modems.

Data Terminal Ready - A RS-232 serial port line which is held high (+3 volts or more) when the terminal is turned on and available. This is one of the handshaking lines. A device wanting to communicate with the terminal may check the status of this line to determine if the device is available. For more information see the FAQ RS-232 That Works! In our Technical Library.

A device without a microprocessor. A dumb serial card is a card which has only UARTs, but no processor. It depends on the main microprocessor in the computer to service the UARTs.

A single cable containing two fibers in a protective jacket. One fiber is usually used to carry a signal in each direction. A Simplex fiber optic cable contains a single fiber. Fiber can handle serial data or ethernet data depending on the devices. B&B stocks Multimode & Single Mode patch cables with common connectors such as ST, LC & SC.

A ground that directly connects to the earth though grounding stakes and buried copper wire or metal water pipes buried in the earth. Usually some form of earth ground is provided at the entry point of phone lines or AC power. The power ground within a building can vary from earth ground, and earth grounds at different locations can have voltage differences between them, especially during electrical storms.

1. In a half duplex 2-wire 485 system, the receiver is normally disabled during transmit, so the data is not echoed back to the receiver even though the receiver inputs are connected to the transmitter outputs. A Echo Off switch or jumper (if provided) can set the receiver mode so that transmitted data is not fed back to the receiver. It sets the receiver for 2-wire RS-485 mode.
2. A communications terminal program may depend on the remote terminal to echo the characters typed locally. If the program displays the typed characters, and they are echoed by the remote device, each character is repeated (shown twice - sshhoowwnn ttwwiiccee). The Echo off setting turns off local echo so only the returned characters are displayed. The reverse case is that the remote terminal does not return typed characters, and the user can't see what he/she is typing. Then echo needs to be set on locally.

1. In a half duplex 2-wire 485 system, the receiver is normally disabled during transmit, so the data is not echoed back to the receiver even though the receiver inputs are connected to the transmitter outputs. A Echo On switch or jumper (if provided) can set the receiver mode so that it is enabled all the time, and transmitted data is returned to the receiver. Echo on can be used in 2-wire mode, but since the setting enables the receiver all the time, this setting is typically used in 4-wire RS-485 and RS-422 modes.
2. A communications terminal program may depend on the remote terminal to echo the characters typed locally. If the program does not receive the characters back, the user does not know what is being typed. The Echo On setting turns on local echo so that typed characters can be viewed. displays the typed characters, and they are echoed by the remote device, each character is repeated. If typed characters are repeated twice for each character typed, local echo needs to be set Off.

Variously called, Enhanced Communications Port, Enhanced Capabilities Port, Extended Capabilities Port.

1. An asynchronous, 8-bit–wide parallel channel defined by IEEE 1284–1944 that provides PC-to-peripheral and peripheral-to-PC data transfers.
2. A parallel port standard that provides for automatic background transfer using a computer DMA channel, IRQ and additional input and output port registers. Using DMA transfer under Windows 95/98 can be very fast since once a document is spooled and the header is passed to the DMA circuit, the DMA transfers large blocks of data (350KB per second typical) no matter what else the processor is doing under windows. Other ECP functions are available with some devices if they use Microsoft's ECP standard. ECP mode is available when built-in to the motherboard, or from a ISA bus slot using a parallel card with ECP mode and Windows 95/98. NT 4.0 does not support ECP mode, and PCI cards do not have DMA access.

Electrically Erasable Programmable Read Only Memory - memory that retains data even when the power is off.

Extended Industry Standard Architecture. A 32-bit PC expansion bus designed as a superset of the ISA bus. Designed to expand the speed and data width of the legacy expansion bus while still supporting older ISA cards. ISA bus cards can plug into EISA slots.

Electro Magnetic Interference/Radio Frequency Interference: signals generated by expanding/collapsing magnetic fields such as motors, transformers, arc welding, fluorescent/neon lighting, radio/television Transmitters, motor brushes, lightning.

The level at which a device or signal is unaffected by EMI/RFI

Decoding of the full 16-bits of the ISA bus address and the full 32-bits of the PCI bus address. Some interface cards don't decode the full address. This means that such a card will respond to commands at more than one address, so that conflicts with other cards are more likely. Decoding the full address prevents a card from causing conflicts.

A timer feature used to prevent slave devices from receiving preamble commands, inadvertent switching from binary/graphic file transfers, and inactive slave devices from holding control of the master port. The switch can monitor the data line, if there is not any activity for a specific time it will disconnect from the master. Alternately, the switch can ignore commands for a specific amount of time.

Enhanced Printer Port - a printer port that has additional registers and generates the handshaking signals in hardware. Compared to a standard printer port which requires several port writes and reads for each byte transferred, once a EPP port is set to EPP mode, only one write is needed for each byte. EPP software is required to use the EPP port in EPP mode, otherwise it functions as a SPP (Standard Printer Port) or BPP (Bi-directional Printer Port).

A type of LAN invented by the Xerox Corporation and developed in cooperation with DEC and Intel. The original Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Originally Ethernet was specified to transfer data over thick coaxial cable at a speed of 10 Mbps. Now the term Ethernet typically encompasses all of the versions of the IEEE standard, which has adapted to include higher data rates and different media, including thin coaxial, twisted-pair, and fiber optic systems.

The most common types of Ethernet in use today are 10BaseT, which uses twisted pair cable at 10 Mbps, 100BaseT (or Fast Ethernet), which uses twisted pair cable at 100 Mbps, and 1000BaseT (or Gigabit Ethernet) which uses twisted pair cable at 1 Gbps. Fiber optic cable is also a popular medium for each of the connection speeds.

A device that connects to the LAN with Ethernet connections. It may provide serial services to the network, printer services, CD-ROM services, Facsimile or other services. See Serial Server & Wireless Serial Server.

1. Requires connection of a power source such as AC or DC. The required power source is rated for the type of voltage in volts (VAC or VDC), and the required current in mA (milli-Amps), A (Amps) or VA (Volt-Amps)/Watts.
2. A externally powered converter which doesn't support Port Power must obtain power though connection terminals, a DC Jack or Connector pins. Isolated converters may require port power for the RS-232 side, a power supply for the RS-422/485 side. USB to Serial RS-232, RS-422, RS-485 use the USB power bus to obtain 5 VDC power.

A switch that normally selects a primary data path for serial connections, the selects a secondary data path if the primary data path is lost. The B&B fallback switch supports this mode, or can select the primary data path until the alternate data path is activated, it then selects the alternate path until the alternate device is finished, then the primary data path is reselected. The B&B fallback switch can also be used as a port combiner that selects the primary or alternate when data is ready for transfer, locks out the other path until transfer is completed.

Connector which has a receptacle socket (holes) for pins. When F follows the connector type, the connector is a female connector.

Light transmission through flexible transmissive fibers for communications, imaging, or lighting. Offers significant distance, bandwidth, isolation, and EMI/RFI immunity over traditional copper installations.

A signal converter with fiber optic transmitter and fiber optic receiver for the optical signals and electrical inputs & outputs for another signal format such as RS-232, RS-422, 2-wire or 4-wire RS-485, or ethernet fiber converters.

First In, First Out - FIFO implies a queue and buffer to hold it. The oldest data item in the buffer is the first item retrieved.

Contrast with LIFO (Last In, First Out) which operates like a data stack, items placed on the stack are retrieved first in the order of last first.

A full duplex communications system is able to transmit and receive at the same time. Two communications paths are provided, one for each direction. Examples are RS-232, RS-422 and 4-wire RS-485. (2-wire RS-485 is half duplex) Full duplex is like a two lane highway, one in each direction, half duplex is like a on ramp or off ramp, traffic only goes one way at a time.

A connector with dual male or dual female connectors wired pin for pin. Used to change or connect two female devices together (using dual male) or two male devices together (using dual female).

Global Positioning System - A device which uses 3 or more of at least 24 satellites in orbit to determine the local position on earth of the receiver. 3 satellites are needed for a 2D fix, 4 for a 3D fix which includes altitude. Accuracy of position can vary depending on the location of the satellites used, altitude accuracy for civilian uses can vary by +/- 500 ft. Two frequencies are used, L1 (1575.42MHz) for civilian, L2 for military. The date and time are broadcast for positioning references to downloaded tables used to calculate the position. GPS receiver outputs are used in marine and land based navigation systems which interface to a computer through RS-232 or RS-422/485 or USB serial connections.

When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other. In shielded Ethernet cables the shield should be grounded at only one end.

1. A heavy solid or braided wire cable used to provide a low resistance path from a device to a earth ground. Used with surge suppressors.
2. A conductive wrist strap and grounding cord used to discharge static voltages to ground when handling ESD (Electro Static Discharge) sensitive devices such as interface cards.

In a half duplex communications system a device can either receive or transmit, but not both at the same time. Many radio transmission systems are half duplex because the transmitter and receiver use the same frequency, and while transmitting mute the receiver. A RS-485 2-wire system is also Half Duplex because it uses the same pair of wires to transmit and receive.

1. In a RS-232 serial system, data flow control is performed using the CTS (Clear To Send) and RTS (Request To Send) control lines. The DSR (Data Set Ready) and DTR (Data Terminal) control lines are used to determine if a device is connected and active. Additional lines for DCD/CD (Carrier Detector) and RI (Ring Indicator) are used with modems.
2. In a parallel printer interface, the primary printer handshake lines are Strobe (to printer) and Busy (from printer) and Acknowledge (from Printer). Additional lines are used to indicate Printer Select (printer ready), Printer Error, Paper Error, Reset.
3. Other types of devices may have other handshaking signals, at least one signal is needed to indicate that data is ready to be read, and one signal returned to indicate that data can be received or not received. Some devices have a handshaking mode and a burst mode, data transfer is setup with handshaking, then transferred with a Acknowledge for each byte, which tells the sender to change the data byte. If Acknowledge is not received soon enough, burst mode times out.

The process of using handshaking lines or software data flow control such as X-On/X-Off to transfer each byte of data.

1. Serial Port transfer using the RTS and CTS control lines to control data flow instead of using software flow control using X-On/X-Off control with a full duplex serial link.
2. Parallel data transfer in which handshaking for each data byte is handled automatically by the hardware rather than by computer instructions that alter each of the 4 hardware states

Serial Port transfer using the RTS and CTS control lines to control data flow instead of using software flow control using X-On/X-Off control with a full duplex serial link.

(VGA type) - computer video
High Density 15 pin "D" type connector sized the same as DB9 except more pins

A central connection point for multiple LAN devices in a Local Area Network, a central connection point for multiple USB devices in a USB network. For a USB network, expands the number of USB connections that can be made to one of the host USB ports. Provides one connection upstream, and usually 4 or more downstream connections. Upstream connections go to the host, downstream to additional devices. For a Ethernet Serial hub, provides network connection for multiple serial devices using RS-232, RS-422 or RS-485 signal formats.

Hertz - the term adopted to indicate a rate of cyclic voltage alternations per second in AC (alternating current) signals. The term was formerly known as "cycles per second" which was abbreviated cps and could be confused with another scientific term with a different meaning. Used to indicate the frequency of AC power 50Hz, 60Hz or 400Hz, audio (16Hz to 20KHz) or radio waves such as 520KHz, 108MHz, 900MHz or 1.2GHz.

Input/Output circuit boards or modules used for computer data acquisition or control, typically for digital I/O to read switch closures or control relays.

A set of standards for parallel printer port interfacing and cabling. A IEEE1284 printer cable meets the low capacitance requirements and can permit parallel devices which meet the standard to be separated by as much as 30 feet.

A package which is based on the size of the DB25 or DB9 type connector. The package is about 0.9 inch thick by slightly more than the connector width/height, and is the length of a single or double length connector shell.

DB9 Connector Shell

DB25 Connector Shell

Double DB25 Shell

1. The connection between computer and the outside world. Electrical interfaces can be serial, RS-232, RS-422, RS-485, USB-A Female, Parallel, or similar.
2. A user interface provides a connection between the user and program. It includes the appearance of the screens, menus, mouse/keyboard keys for input/output. Windows provides standard methods for a program to use to build a user interface.

A converter from one type of interface to another. A converter performs conversion from one electrical format to another. RS-232 to RS-422 or RS-485 or back, RS-232 to fiber optic or back. Some converters handle hardware conversion between formats. Some require hardware and software to perform conversion. For example, Host USB to RS-232/422/485 or Ethernet to Serial.

Compare a converter to an adapter. An adapter simply converts hardware connections, whereas a converter may also provide an electrical signaling change. A RS-232 signal may use DB25, DB9 or RJ-11 or phone plug or jack. The signal connector is adapted, not converted.

The IRQ is a hardware Interrupt Request line in a ISA bus expansion slot on a PC or AT compatible computer. The 8 bit PC ISA slot has 8 interrupts, the 16 bit slot has another 7 since one of the first 8 is used to link in the remaining 8. The IRQ line is used by devices to request immediate service by the main microprocessor. When the IRQ line is set, the microprocessor stops whatever it's doing, saves status, checks which line was set, then jumps to code to handle the interrupt. The processor then clears the interrupt and returns to what it was doing before. IRQ lines are set by the internal timer, keyboard, hard drive controller, PCI, USB controller, sound card, serial ports, printer and more. (See Windows Control Panel, System, Device Manager, Computer Properties for a list)

Industry Standard Architecture bus - the 8-bit or 16-bit internal expansion bus used on the IBM PC and PC/AT. Standard bus speed is 8 MHz (after the second version 8MHz IBM AT computer). This is the bus used on 386/486 compatible computers and ISA bus computers which followed. Later computers added a different expansion bus for faster Video and sound processing, the 33MHz PCI bus.

A UART based protocol used in vehicle communication. A subset of this protocol (ISO9141-2) is used by CARB (California Air Resources Board) and the EPA as an acceptable diagnostic communications protocol used to request, retrieve, and reset emissions related functions.

Separation of all electrical signals and ground on one device from those on another device. Isolation is usually rated in volts or leakage currents. Isolated power is typically handled by power transformers and separate power supplies with no common between one side and the other. Signal lines may be isolated with signal transformers (depending on the signal), optical isolators, or with fiber optic converters.

A heavy duty vehicle bus specification defined according to SAE J1708 standard. J1708 is physically similar to RS-485, but with changes in the biasing and filtering to add Collision Detection and Multiple Access capabilities.

The J1708 specification requires that various nodes on the bus use a priority system for bus access. It is important that you use the correct priority for your application to prevent excessive bus collisions and retries.

A heavy duty vehicle bus specification defined according to SAE J1850 standard.

A heavy duty vehicle bus specification defined according to SAE J1939 standard. J1939 is based on the CAN physical layer.

kilo (1000) bits per second - data rate

See the DIN and Mini-DIN Adapter cables

Local Area Network

Light Emitting Diode - a diode that outputs light when forward biased, may be infrared, red, green or yellow. Solid State replacement for bulb indicator lamps. Forward voltage drop is typically 1.9-2.4 volts, making them suitable indicators when used with a current limiting resistor for low current TTL indicators or RS-232 signal indicators. Handy for Data Acquisition digital indicators.

Multiple Light Emitting Diodes - used for indicators of data, power or status.

Light Emitting Diodes (LEDs) can give an instant visual indication of system operation. Many of our converters are available with LED’s to assist in troubleshooting and inspection (and blinking lights will always impress the boss).

TD LED lights when data is sent

RD LED lights when data is received.

1. Mode of B&B automatic fallback switch that latches to the first port that asserts itself, and maintains the connection until disasserted.
2. When two users share one device such as a modem or serial printer or other serial device. Each user must be aware and not send data to the device while the other user is accessing it.

A device that allows two computers to share one device without manually having to switch between user A and user B. It typically has connections for two computers, one device.

The connector which has the plug portion or pins which fit a female receptacle or socket. The plug which inserts into a jack. Usually M after the connector type indicates a Male connector.

Many products such as printers place the female socket on the device so that if a pin breaks or is bent on a cable, the cable is more easily replaced than the connector built-in to a device. The exception is RS-232 serial connectors, which are male to avoid confusion with the female DB9 video connector and female DB25 printer connector.

The master in a network controls all the other devices (slave devices) attached to the network. The master sends commands to request data, the slaves respond with data. Some slave devices may prefix their response with an identifying header.

In a Smart Switch, this is the primary port connection to the host and the port which accepts commands to select other ports (slave ports) such as A, B, C or D.

A command/response relationship between two devices where one device sends commands and requests data (Master). The other device only responds to the commands (Slave), and does not initiate conversation.

Maximum baud rate supported by the hardware (electronics circuitry)

Mega bytes per second - data rate in million bytes (8 bits)

Mega bits per second - data rate in million bits

1 meter is 100 cm or 1000 mm or about 3.28 feet (ft) or 39.37 inches.

Conversions:
multiply meters by 3.28 for feet or by 39.37 for inches
1 inch (" double quote) = 25.4 mm or 2.54 cm - multiply inches by 25.4 for mm or 2.54 for cm
1 foot (ft.) (' single quote) = 12 inches = 0.3048 meter - multiply ft. by 0.3048 for meters.
1 statute mile = 1.61 km
Weight:
1 pound (lb.) = 16 oz. = 0.4536 kg
Volume: (Engine Displacement)
1000 cc = 1 liter (lt.)
cubic centimeter (cc) = 0.0610 cu inch
Example: 305 cu inches divided by 0.061 = 5000 cc or 5 lt.

RJ-11 or RJ-12

The main board in a personal computer which usually contains the main microprocessor and expansion slots or built-in hardware for input, video, hard/floppy drive control, output.

1. Multiple devices at various locations connected in parallel or acting similar to parallel devices.
2. A RS-485 network (2-wire or 4-wire) with multiple devices in parallel at various locations.

Analog or digital readout meter which can read a range of AC/DC Voltages, Ohms, Current. May include special functions for Frequency, transistor gain, DB, diode checking, continuity.

A type of optical fiber that provides many internal reflective paths (modes) to transfer light. Light enters and leaves the fiber at different angles. Because light traveling in different paths takes different amounts of time to reach the end of the fiber, the bandwidth is lower than for single mode fiber. Because of it’s comparatively large core diameter, an inexpensive LED light source can be used, making multimode fiber popular for serial communication, LANs, and other applications where bandwidth is not the major concern.

1. A device which allows several data channels to be carried by one main data channel. Up to 16 Teletype data channels can be carried in the bandwidth of one voice channel, in Frequency Shift Multiplexing, one long distance data communications link could carry 4 voice channels or 64 TTY channels. Time Division Multiplexing is another type of multiplexing.
2. A device such as a smart switch that can select different serial ports to communicate with one device connected to each port. "Multiplexing the port" but not true multiplexing.
3. A B&B Buffered Smart Switch that can be connected "back-to-back" to another of the same switch. It is set up to poll the 4 slave ports at a slower rate, transfer data out the master port through a high speed link (at least 4 times faster data rate than the slaves), then separate the data back out to 4 slave ports using the second switch.

A standard describing the electrical characteristics and the software protocol used for interfacing electronic marine equipment.

Each driver/receiver pair on a RS-485 bus is a node on the network. Up to 32 nodes can be connected in parallel before adding a repeater. One repeater equates to two nodes, one on each side.

A device or converter that has signal grounds or power sources in common between the input and output sides or between the RS-232 and RS-232/422/485 sides.

Memory which retains data even when power is turned off.

A null modem cable or connector permits two similar RS-232 Devices (wired as DTE or DCE) to be connected together so that the outputs of one device are routed to the inputs of the other device. At a minimum, the Transmit Data (Tx) of one device is routed to the Receive Data (Rx) of the other, and the Tx of the second device to the Rx of the other, and the ground lines are interconnected. Various configurations are available (See 232MFNM Data Sheet).

RS-232 devices may require DSR cross connected to DTR, and to CD, and RTS to CTS. (note that a regular MODEM cable has connections to the same pins on both sides)

Full pinouts below:

DB9 Wiring - Full Handshaking
CD #1 jumpered to #6 (both connectors)
Rx #2 to #3 Tx
Tx #3 to #2 Rx
DTR #4 to #6 DSR
GND #5 to #5 Ground
DSR #6 to #1 CD
RTS #7 to #8 CTS
CTS #8 to #7 RTS
RI #9 not connected

DB25 Wiring - Full Handshaking (Model 232DTE)
Shield #1 to #1
Tx #2 to #3 Rx
Rx #3 to #2 Tx
RTS #4 to #5 CTS
CTS #5 to #4 RTS
DSR #6 to #20 DTR
GND #7 to #7 Ground
CD #8 to #20 DTR
DTR #20 to #6 DSR
DTR #20 to #8 CD
RI #22 not connected

On-Board Diagnostics, Standard II.

Congress passed the Clean Air Act in 1970 and established the Environmental Protection Agency (EPA). This started a series of graduated emission standards and requirements for maintenance of vehicles for extended periods of time. To meet these standards, manufacturers turned to electronically controlled fuel feed and ignition systems. Sensors measured engine performance and adjusted the systems to provide minimum pollution. These sensors were also accessed to provide early diagnostic assistance.

At first there were few standards and each manufacturer had their own systems and signals. In 1988, the Society of Automotive Engineers (SAE) set a standard connector plug and set of diagnostic test signals. The EPA adapted most of their standards from the SAE on-board diagnostic programs and recommendations. OBD-II is an expanded set of standards and practices developed by SAE and adopted by the EPA and CARB (California Air Resources Board) for implementation by January 1, 1996.

A Omni directional antenna radiates with equal power in all directions parallel to orientation, and is equally sensitive to signals parallel to orientation from all directions. Pattern is doughnut shape

A circuit board with all the components mounted but which does not have a case or cover. Mounting into a case can be performed with standoffs and mounting hardware such as screws & nuts or the board can be mounted in a DIN rail rack with a Extruded PVC SNAPTRACK 12 inch mounting Extrusion and DIN Rail adapter clips.

Open Board

Software which permits a computer to start up, read keyboard characters, save files to floppies, a hard drive or removable media, to display or send characters or graphics to a printer or display, access serial ports, USB ports, support various displays and graphics modes/graphics depths.

Various Operating Systems include CPM, MS-DOS (Versions 1.0 to 6.2), TRS-DOS, GEM, AmigaOS, OS-9, RTOS, UNIX, Linux, SCO Unix, Solaris, OS/2, MacOS, Windows 95/98/2000, Windows NT 3.51 & 4.0 and many others.

Software drivers for a hardware device permit a particular OS to use the hardware and have it function in normal manner taking advantage of functions built into the OS.

Electrical isolation provided by converting the electrical signal to light, then converting the light back to electrical signal. The optical isolator consists of a light emitting diode and phototransistor in one package. This is a better method of providing circuit isolation for some types of signals than by using signal transformers, radio frequencies or surface wave/acoustic isolators.
How Optical Isolation Works - Illustration

The type electrical connections used to connect to the relay contacts or coil.

Enclosure style

Box with Terminal Blocks

DB9 In-Line Connector style

DB9 In-Line Connector style with Terminal Blocks

DB25 In-Line Connector style

DB25 In-Line Connector style with Terminal Blocks

In-Line Connector style with Terminal Blocks and Slide on Cover

DIN Rail Package

Pocket Size Case

Open board is no enclosure with holes for mounting with stand-offs or a DIN Rail holder for PCB (Printed Circuit Board) or PWB (Printed Wiring Board).

A parallel port consists of electrical connections which permit the computer or device to transmit/receive several bits at once to another computer/device. As opposed to serial ports which transmit one bit at a time in sequence.

A Standard Printer Port (SPP) transfers a byte (8-bits) at a time in parallel with handshaking. The data lines used consist of bits 7-0 (8-bits), control lines (Strobe/Command), Auto Linefeed, Initialize, Select Printer, and status lines from the printer, Ack (acknowledge), Busy, Paper Error(Out/End), Select (Printer Selected), Error/Fault, The Printer interface usually follows the Centronics standard for connector (36 pin Amphenol bail lock female/socket) and pinouts, the computer generally follows the IBM PC standard for printer port connector (DB25F) and pinouts.

Standard DB25M to C36M cables were available in Dec 2011 from www.jameco.com B&B quit stocking them in about 2001.

Parallel printer port types include BPP (Bi-directional Printer Port), EPP (Enhanced Printer Port), and ECP (Enhanced Capabilities Port).

Current Loop - When one side of the current loop is passive, the other side must supply the current source. There is usually a transmit loop and receive loop on any one device. Either or both can be passive. Current flows during a During a "MARK," “IDLE,” or “1” state. During a "SPACE," “START,” or “0” state, no current is supplied. Refer to our Current Loop Application Note for more info.

1. A trademark of PCMCIA. A removable device that is designed to be plugged into a PCMCIA slot and used as a memory-related peripheral.
2. A PCMCIA (Personal Computer Memory Card International Association) card.
3. This term must be clarified as to whether PCMCIA is intended or another type of card for a PC compatible computer, such as ISA, MCA (Micro Channel Architecture) EISA or PCI.
4. Any expansion card that might be used in a personal computer. The PC is first IBM Personal Computer sold in August '81. Expansion cards for the PC fit in one of the five 8-bit PC bus connector slots, (now called 8-bit ISA bus slots). The PC/AT provided 16-bit AT bus slots which are 8-bit slot compatible.

A internal 32 bit expansion bus used in Intel compatible personal computers. The bus speed is 33 MHz or 66 MHz, four times or eight times faster than the 8 MHz IBM AT bus now called ISA. The connectors on PCI bus differ from ISA, EISA, or Micro Channel busses. Most year 2000 computers with expansion slots have PCI slots.

PCMCIA (Personal Computer Memory Card International Association) - A type of expansion slot used on laptop/portable computers which can accept memory, serial, printer, SCSI or other types of adapters.

A relationship between two devices where either can request data from the other or send data. Either unit can act as a master and initiate communication. Same as master-master.

used for video and audio component connections

A labeled figure or numbered list/diagram showing pin layout/index or which shows the signal name and pin number for each connection to a device. The pinouts on a device help technicians to wire connectors or cables and to make the proper signal connections (or omit connections) between devices. Pinouts on many devices such as RS-422 or RS-485 are non-standard, so diagrams are usually needed unless the connection copies a widely accepted product such as the parallel printer Centronics connections on a printer (some may be added or omitted), or the IBM PC printer connector (DB25F), or the RS-232 DB25M (PC) or DB9M (PC/AT). As the old saying goes, "The nicest thing about Standards is that there are so many of them!"

B&B Electronics customers often order Custom Products with pinouts for the Standard they need to connect to. Some products with special pinouts become standard products.

Programmable Logic Controller - a microprocessor controlled device that locally controls some process and usually connects serially to another device or network of other devices. Usually includes a RS-232, RS-422 or RS-485 serial connection.

Rating for cable which is fire resistant and less toxic when burning than non-Plenum rated cable.

Male connector with pins or prongs for contacts. Fits in female/socket/receptacle/jack

See Plug and Play

1. Descriptive term used for easy to install computer hardware that usually worked without any special configuration in DOS or other computing environments prior to Windows 95.
2. Plug and Play is the technology that supports automatic configuration of PC hardware and attached devices. A user can attach a new device such as sound or fax/modem card ("plug it in") and start using it ("begin playing") without having to configure the device manually (using switches or jumpers to select the I/O address, IRQ, memory address, DMA channel). Plug and Play technology is implemented in hardware, in the operating system, and in supporting software such as drivers and BIOS.
   
   First introduced for PC compatible hardware with Microsoft® Windows® 95, and supported with Windows 98, true Plug and Play configuration capabilities are supported under Windows 2000. For Plug and Play and power management support under Windows 2000, the system and its BIOS must be compliant with Advanced Configuration and Power Interface Specification (ACPI).
   
   Plug and Play technologies are defined for USB, IEEE 1394, PCI, ISA, SCSI, ATA, LPT, COM, and PC Card/CardBus. Each Plug and Play device must have all of the following capabilities:
   (a) It must be uniquely identified.
   (b) It must state the services it provides and the resources it requires.
   (c) It must identify the driver that supports it.
   (d) It must allow software to configure it.
   
   For more information regarding Plug and Play specifications and programming, visit the Microsoft Websites.

See Plug and Play

See "Plug and Play"

A design philosophy and set of specifications that describe hardware and software changes to the PC and its peripherals that automatically identify and arbitrate resource requirements among all devices and buses on the system. Plug and Play specifies a set of API elements that are used in addition to, not in place of, existing driver architectures.

The checkout counter location where the customer gets the total due and pays. Location of barcode scanners and cash register, credit card/ATM debit card readers/terminals.

Barcode scanner used at checkout.

Communication from one device at one location to another device at a second location. Two devices rather than multi-drop devices.

1. Electrical interface on a computer or device which permits connection to another device. Usually, Serial/RS-232, Parallel Printer, Video/VGA/SVGA, SCSI, Keyboard, IR, USB, Audio, Firewire, Joystick/Trigger/Game/Controller, Mouse, Ethernet, PCMCIA, Telephone Modem, or Cellular Modem port.
2. Electrical connection on a microprocessor that permits the processor to read inputs or control outputs.

A serial device that allows two or more serial devices to alternately share a single port on a host computer.

1. USB device that obtains power from the USB port power lines.
2. A serial/fiber optic/parallel converter which obtains operating power from the input signals and handshaking lines. It 'steals' power from the device to which it is connected so that it can power it's own low power circuitry.

For more information, refer to the B&B Technical Article, "Tips for Using Port Powered Converters"

1. USB Converter that obtains power from the USB port power lines.
2. A serial/fiber optic/parallel converter which obtains it's operating power from the input signals and handshaking lines. In Serial Converters, TD/Tx, DTR, RTS or the DTR/DSR and RTS/CTS/CD pairs. The necessary lines must be present and connected, they must provide enough voltage (6-7 volts) when loaded, some models require positive voltages on RTS and DTR, others use either positive or negative voltages.

B&B has many converters than can derive all the power they need for operation from the host RS-232 port. We call these converters “Port Powered”. In order to use a Port Powered converter, the host RS-232 port must meet true RS-232 voltage levels of +- 10V or greater open circuit. Some battery powered PC’s such as handhelds use a low power version of RS-232 which isn’t capable of driving Port Powered devices. Recently, IBM has been implementing these low power ports on their desktops as well.

Other converters require a DC power supply. The acceptable voltage range is listed for each of these models. We have power supplies available for all of our converters. Click on the model number of the converter for detailed information and the part number of the recommended power supply.

A multiple character sequence used to select a addressable device such as a Smart Switch or RS-485 addressable device. Usually a unique 3-4 byte command sequence that differs for each addressable device or port. Often called a Header, since the body of the command or data is the same. String data represents characters, 7 bit data has character values 0-127, 8 bit data has character values of 0-255. Printable characters range from 32 dec (space) to 126. Refer to our B&B Technical Library EIA Card for the characters and values.

One of the modes in the B&B Fallback switch that defaults to the primary port enabled. Only switches to the alternate port when the alternate port is asserting itself and the primary port is not.

A B&B Printer Data Splitter allows two computers/devices to alternately share a Serial Printer. A Switchbox with A/B switches is usually needed to share a parallel printer, but networking or other printer sharing devices are available.

The electrical connection on a computer intended for a printer. May be a serial printer port (RS-232, RS-422 or AppleTalk/422), a SCSI printer port, USB printer port, or parallel printer port. Today, proprietary interfaces for a printer are generally converted to serial or Centronics parallel so a hardware manufacturer does not need to offer a proprietary printer..

Microprocessor - (µP) the CPU (Central Processing Unit) for a device.

Protocols are like languages, French, English, Spanish, Chinese or Japanese. If devices are to understand each other, they must speak the same language, similar to using a phone, or a translator is needed. Interfaces such as RS232, RS422, RS485, or Ethernet TCP are the electrical interface. Modbus has several types, ASCII, RTU or Modbus/TCP. Modbus Bridge units bridge between serial and Ethernet Modbus protocols. Gateways bridge between different protocols, enabling a device using one protocol to access data in a different protocol and electrical interface. The Gateway needs to know both protocols with drivers to translate; masters can share data with another master.

Another way of thinking about protocols is the list of commands the device will respond to and the data to be returned for each request, and format of response. Each device may have differences, model to model, but usually a family follows the same format for a series.

A Radio Frequency transceiver (transmitter/receiver) for serial data. A Radio Modem connects to a RS-232 serial port or RS-422/485 port and transmits & receives signals to/from another matching Radio modem. Some Radio modems are full duplex, some are half duplex. Example ZP9D-115RM-LR.

Receive Data line - Receive/Rx

Receive Data line A. One of two differential receive lines in RS-422 or 4-wire RS-485 connections. The (-) line which is low compared to the (+) B line during the Mark/Inactive state.

Receive Data line B. One of two differential receive lines in RS-422 or 4-wire RS-485 connections. The (+) line which is high compared to the (-) A line during the Mark/Inactive state.

The connector type on a Watchdog card which connects to the reset or computer power supply control circuitry connector.

A female (socket/jack) connector that accepts pins

Electrical contact switch that is activated/deactivated by current flow in a coil. May be SPST, SPDT, or DPDT (single pole single throw, single pole double throw, double pole double throw)

A device which receives input in one format and restores the signal to standard levels. May be for RS-232, RS-422, RS-485 or fiber optic signals. Repeaters are used to increase the number of devices connected to a RS-485 network or to increase the connection distance by strengthening signals weakened by long transmission distances (over 50 ft. for RS-232 or 4000 ft for RS-422 or RS-485 communications).

Radio Frequency signals. Electromagnetic signals in a radio band.

A Radio Frequency transceiver (transmitter/receiver) for serial data. A RF Modem connects to a RS-232 serial port or RS-422/485 port and transmits & receives signals to/from another matching RF modem. Some RF modems are full duplex, some are half duplex. Examples: ZP24D-250RM-SR or ZP9D-115RM-LR

Radio Frequency Interference: Noise or signals in a radio frequency band which originates from one device and causes another device to operate poorly. May be generated by expanding/collapsing magnetic fields such as motors, transformers, arc welding, fluorescent/neon lighting, radio/television transmitters, motor brushes, lightning, computer equipment, and serial data transmission.

A modular telephone style 4-contact connector. Usually Male on the connecting cord, female on devices. The center 4 positions have contacts similar to a residential telephone or telephone modem. This is a connector type only. Devices that use this connector are not necessarily designed for connection to telephone company phone or data lines.

A modular telephone style 6-contact connector. Usually Male on the connecting cord, female on devices. The contacts are similar to a residential telephone or telephone modem, but one more contact is at each end. This is a connector type only. Devices that use this connector are not necessarily designed for connection to telephone company phone or data lines.

A 8-contact connector type most often used for unshielded twisted pair LAN wiring between a computer and LAN wall outlet connector. Devices that use this connector are not necessarily intended for electrical connection to a LAN. Some RJ45 connector cables have 10 pins.

RS-232 provides serial connections using single ended signals, which may vary between -3 to -25 volts to +3 to +25 volts.

Minimal signals for bi-directional communication are signal ground/common, Transmit (Tx) and Receive (Rx) Data or TD and RD. IBM PC compatible RS-232C ports provide handshaking lines, DSR and DTR and flow control handshaking lines, CTS and RTS. Modem control lines for RI (Ring Indicator) and CD (Carrier Detector) are supported. Data is transferred serially using Asynchronous data, with a start bit, data bits, stop bit/bits.

Flow control can be performed by software using X-On/X-Off, or by hardware handshaking if available.

There is no standard pinout or connector specified, most companies followed the IBM PC XT/AT DB25M or DB9M but RJ12/RJ11, DB9F or RJ45 connectors can or have been used.

This is the connector used on the RS-232 side of the converter or a RS-232 device.

A electrical connector that provides some or all of the RS-232 signal lines. Unless a device is transmit or receive only, a RS-232 port will provide at least signal ground/common and Rx & Tx.

A fiber optical converter which has dual interfaces can be set to convert from RS-232 to fiber optic at one end and from/to RS-422 or 4-wire RS-485 or 2-wire RS-485 at the other end. If using for 2-wire RS-485, the devices must be suitable for half duplex operation.

A standard used to extend serial communications up to 4000 ft. between two devices. Each channel of communications is converted to a differential signal and carried on a twisted wire pair so that when the differential signal is received, common mode noise is rejected. RS-422 generally has at least two channels, Receive and Transmit. These are carried on 4-wires, and a signal common/ground provides a reference for the receiver and transmitter. RS-422 can also handle handshaking signals using additional twisted pairs. Signal levels at the transmitter when active during SPACE are +5 volts (TDA ) and 0 volts (TDB) or during MARK, 0 volts (TDA) and +5 volts (TDB).

For more information, refer to the B&B RS-422/485 Application Note & EIA Card listing EIA-530 pinouts another standard was followed for SMPTE standard for time codes & video editing equipment. Adopted by Sony and film camera companies.

This is the connector type used on the RS-422 side of a converter or device.

A serial port which provides RS-422 differential inputs for receive and outputs for transmit. Typical RS-422 ports support 2-channels.

Some RS-422 devices can have the transmit driver enabled and disabled as is done for RS-485. Disabling the transmitter when not used saves power on port powered devices. It also allows a RS-422 device to operate as in a 4-wire "half 485" mode, the same as a 4-wire RS-485 device.

Normal RS-422 devices have the transmitter enabled all the time. Controlled transmitters are activated by setting the RTS line in the RS-232 device or the RTS control in the UART. When the RTS line is not asserted, the transmitter is set Off to a high impedance state.

RS-485 is a multi-drop extension to the RS-422 standard. It uses differential signals on twisted pairs for receive and transmit. The RS-485 IC is a superset of RS-422 except RS-485 supports on TD & RD

RS-485 systems can be half duplex 2-wire systems (one twisted pair plus signal common/ground) or full duplex 4-wire systems. A RS-485 transmitter driver is activated to send data and is set to a high impedance tri-state at the end of transmission. Driver control can be automatic using a Send Data circuit, or manual by setting the RTS line or UART RTS control high for transmit, then low at the end of transmission. In a half duplex 2-wire system, the receiver is set to receive except when transmitting.

In a 2-wire system, all slaves and masters are normally in the receive mode. When one master transmits, all slaves and masters receive the signal and response, and all slaves must be able to ignore commands and responses to/from other slaves. Each slave must wait until transmit is finished plus a delay (for bus turn-around), before responding.

In a 4-wire system, all slaves are connected to the transmitter of the master(s). All slaves connect to the receiver of the master(s). Each slave must respond only to commands addressed to it, but no turn-around delay is needed. The slave can start responding immediately, even while receiving. Other slaves never hear each other's responses.

This is the connector used on the RS-485 side of the converter or device.

A device intended for use in a RS-485 network to isolate a node which has become stuck in a MARK or SPACE state or which has lost power and is loading down the rest of the 485 network so other devices cannot be accessed. When a node stops working, the Port isolator disconnects it from the remainder of the network. Example model: 485OFS

The RS-485 wiring and slave devices interconnected to one or more masters. The number of devices on a RS-485 network is only restricted by the addressing scheme of the devices, typically 255 for a single byte address. Up to 32 nodes can be tied directly together before a repeater or isolated repeater is required.

Electrical connections that provide 2-wire half duplex RS-485 signals or 4-wire full duplex RS-485 signals.

A low voltage implementation of RS-232 in which the maximum signal level is 3.5 volts.

Request To Send - a RS-232 port handshaking line that is typically asserted (raised high) to notify another device that the asserting device would like to transmit data. Is also used in some applications to indicate that the asserting device is ready to accept data.

Some RS-422 and RS-485 Converters use RTS to enable transmit when Asserted (RTS High), and in 2-wire RS-485 systems to disable receive. When RTS is Low, receive is enabled, transmit is tri-stated off. Special software is required to use RTS control. Compare to automatic Send Data(SD).

Receive or receiver - when Morse code was used, the letter X was commonly keyed rather than the full word, Rx rather than receiver, Tx rather than transmit/transmitter. Label for receive line pinouts.

Society of Automotive Engineers - One useful function of such engineering societies is to establish and promote standards that can be adopted by members and industry without regard to a particular manufacturer or product brand.

A CAN (Controller Area Network) based communications protocol. The J1939 is broken down into subsets used in the heavy trucks, agriculture, and industrial equipment industries.

1. Security related products include serial controlled video cameras, remote controlled camera housings, video recorders, Digital Time Lapse Recorders, VCRs, badge readers, access control, security gate controls and related products.
2. A device that responds only to commands that contain the security access code.

Automatic Send Data control. Circuitry for a RS-485 transmit line driver which enables the transmit driver for transmit, then returns the transmit driver to a high impedance tri-state at the end of transmission.

Input devices which are used to sense temperature, pH, flow, pressure, level, light level, noise, proximity, capacitance, mass, frequency, rotation, speed, oxygen or other gasses, smoke, radiation, or related factors which can be detected/sensed.

The connector used for serial connections to/from a device is typically a standard type of DB9 or DB25, but various connector types may be used, RJ-11/RJ-12, 8-pin DIN, RJ-45 or DB37, or USB to Terminal Blocks.

Common serial ports are RS-232, but RS-422 or RS-485 ports are available using expansion cards or converters.

A USB port is serial, but is generally called a USB port, for Universal Serial Bus since the port provides for external system expansion rather than internal expansion using ISA or PCI bus. USB is a host/device bus, not a device/device serial connection.

A hub connects multiple serial port devices to a network.

Usually a RS-232C serial port, but may be RS-422 or RS-485 connections. The electrical connections to a computer or device

In a serial port, a byte of data is transmitted or received one bit at a time. Typical 8 bit data requires that 10 bits be transferred, one bit at a time. In a 8 bit parallel port, data is transferred 8 bits at once.

A USB port is a special type of host computer serial port. USB downstream devices can communicate with the host, but not with each other.

Signal Ground (SG) is the signal common for a serial or similar connector. Single ended signals are referenced the common, and differential signal receivers require the common reference to establish the common level between transmitter and receiver. Signal Ground may be isolated from the grounds on other devices or may be connected by some device or devices to Earth or AC mains ground. Signal Ground may be used as a reference to the (-) minus side of a power supply.

Shared Interrupt Request (IRQs) lines - When several computer devices or PCI slots use the same IRQ, they are sharing it. Serial Cards with shared IRQs can use one IRQ for 1-4 serial port UARTs. Hardware IRQ sharing may require hardware and software support, else only one device can be actively using that IRQ at a time. USB host controllers share IRQ's.

Operating single direction or half duplex. A single fiber optic cable is a simplex cable.

A type of optical fiber with a very small core diameter that provides only one internal reflective path (mode) to transfer light. Light enters and leaves the fiber at only one angle. Because the light has only one path, the bandwidth can be much higher than for multi mode fiber. Because of it’s comparatively small core diameter, a laser light source is typically used. This makes single mode fiber popular for more bandwidth intensive applications, such as telecommunications. Ethernet devices can communicate 15km or more, Multimode is 2km at 100BaseFX.

A device which responds to commands by performing some action or returning data. A slave does not send data until data is requested.

In a Smart Switch, the master port is the controlling port which accepts commands and selects port A, B, C, or D for connection. The Slave port is the selected A, B, C or D.

A device which has a microprocessor is considered a Smart device. Without a microprocessor, it is a "Dumb" device.

A B&B Electronics device that allows you to control or monitor multiple serial devices with a single port. Sometimes called a "code activated switch" or "sharer"

This mode allows the RS-232 slave ports to connect with the master by asserting the RTS or CTS. The way a slave connects with the master varies with the model of smart switch being used. The master, with a designated command string can also select a port in this mode of operation.

In the smart switch mode, the device connected to the master port controls communication with the slave ports. The smart switch will constantly monitor the data flow looking for a command string to direct its operation. The command will instruct the switch to connect a specified slave port to send or receive data to the master.

Society of Motion Picture and Television Engineers - One function of such societies is to discuss and establish standards which can be used by others working in the same areas. Well known SMPTE standards include time codes used to synchronize picture frames and sound for film or video production. Another standard recommends pinouts for RS-422 video editors and related video equipment.

Female connector which accepts pins - Receptacle for Jack or Plug

A sequence of bytes, which is recognized by a device as a command parameter data. The characters and sequence is unique for various devices. Common printer sequences start with Esc (27 decimal), other devices use non-printable characters (such as STX & RTX) to mark the start and end of the data, and use printable characters to encode parameter data. Most B&B device command sequences are 4-6 characters for the command and data.

A software controlled device must be controlled by custom software that specifies that particular device or the customer/engineer must provide for custom programming that controls the device according to application needs.

copper pads to solder wires to

A transmitted signal that rather than using a limited fixed FM or AM signal frequency or channel, spreads the signal over a wide spectrum/range of frequencies during transmission. The receiver concentrates/compresses frequencies during reception, then recovers the information.

A commonly used optical fiber connector for both Multi-mode and Single-mode fiber. Used in many LAN installations and is the standard connector supplied on B&B fiber optic converters and cables.

Surge protection stages - one stage is usually a Transient Voltage Suppressor that clamps or limits the maximum voltage by conducting positive or negative voltages above a threshold voltage to ground or to the connection at the other side. A second stage may be a fuse or resistor in series with the signal line before the TVS. Extremely strong voltages or currents my open the fuse or be dropped across the resistor. A third stage may be a gas discharge device or neon device which breaks down and conducts above 72-90 volts. This can discharge high static voltages.

The Command line in a parallel printer interface. When the strobe is not asserted, the printer ignores data or changes on the data lines. After a byte is output to the data port, the Strobe is asserted to tell the printer to read the data. When the printer starts to read and process the data, the printer sets the Busy line to busy state, then processes the data. At the end of processing, the printer toggles the Acknowledge to acknowledge state for a certain time, then returns to non-acknowledge state and clears the Busy line. The strobe line is then changed to non-strobe condition, and the next byte can be placed on the data bus. See 232SPS2 Serial/parallel converter.

Suppression limits the voltage on the input lines. Suppression attempts to clamp or conduct voltages between lines on one side of the suppressor. High voltages and heavy currents may exceed the rating of the device, causing it to short or open, which is one reason some current limiting may be provided by fuse or resistance. The suppressor may become faulty while attempting to protect, so it may need to be replaced after a heavy surge or lightning.

A abnormal current or voltage that exceeds the normal maximum rating of a device.

Protection of a device from abnormal currents or voltages so that it is not damaged, and will be likely to operate normally after the short term condition ceases.
How Surge Protection Works - Illustration

A device which suppresses voltage or current surges on serial data lines, AC input power lines, telephone/Facsimile lines, or antenna/cable TV lines.

A power supply that operates by turning off/on rapidly (switching) to convert DC to AC at some frequency (usually 15.734KHz or less) that can use a small core transformer. The AC is then rectified back to DC. The DC voltages on the secondary side may provide feedback to the primary side for voltage regulation. The transformer provides isolation. Optical feedback isolates the secondary side from the primary side. A switching supply for AC line power usually converts the AC to DC before converting it back to higher frequency AC, then DC. Many AC supplies are designed for Worldwide power and handle 240/220/120/100 VAC at 50/60Hz.

A DC/DC converter is a switching supply.

A set of protocols that permit physical networks to be joined together to form an internet. TCP/IP combines the individual networks to form a virtual network in which individual hosts are identified not by physical network addresses but by IP addresses.

Transmit Data (Tx) - The Data Output line on a Computer/DTE device, the input line on a Modem/DCE device.

The (-) line in a RS-422 (or 4-wire RS-485) transmit pair. This line is minus relative to the TD(B) line during a inactive or MARK state.

The (+) line in a RS-422 (or 4-wire RS-485) transmit pair. This line is positive relative to the TD(A) line during a inactive or MARK state.

Telephone Company - a modem or device intended for use with Plain Old Telephone Service (POTS) lines can use standard dial up telephone lines normally used for standard voice telephone.

A Control that can be activated based on phone rings and/or DTMF (touch tones).

Connection terminals which provide electrical contacts for tinned stripped wires, with some means of tightening or loosening the connection to the wires.

B&B devices using terminal blocks have a hole to insert the wire, and a screw to tighten/secure it. The hole can usually accept one or two wires. Some surge protection devices use a Terminal Strip, usually called a barrier strip. It accepts wires with a three-quarter wrap around the screw or lug.

Connecting a resistance at one or both ends of a cable to prevent reflections is called Termination. The proper termination resistance is equal to the characteristic impedance of the cable. Reflections travelling up/down the line can alter the signal and the effect can be similar to Ghosting of a TV signal.

Typical RS-422/RS-485 cables may require a 120 ohm termination at each end of a cable run if reflections cause a problem. Termination (when needed) is normally installed on the receivers at each end. Some B&B converters/cards provide selectable termination using a jumper or switch, others provide extra terminals in parallel for connection of termination.

Common termination values for electronic devices varies by the type of device, 75 ohms for video or RF antenna, 300 ohms for twin lead, 50 ohm for coax, and other values of pull-up/pull-down termination for SCSI bus devices.

Dual Tone Multi-Frequency (DTMF) - two tones of a set of 8 tones are generated by a DTMF keypad. Each row (1, 4, 7, star) activates one tone, each column (1, 2, 3, A) activates a second tone. The standard telephone keypad omits column A (A, B, C, D). DTMF tones can be carried by voice links, and they are generated by most telephones and telephone modems.

A combination radio transmitter and receiver

Transistor Transistor Logic - logic levels for TTL digital ICs are typically +5VDC and 0VDC. The logic low must be less than 0.6 volts, the high over +4 volts. Input levels in between may be indeterminate, resulting in outputs either high or low.

A device that suppresses voltages by conducting either positive or negative voltages above the threshold voltage from one terminal to the other. Electrically, a TVS works like back-to-back Zener diodes.

A cable for serial communication which includes at least one twisted pair of two wires. May be shielded or may provide a separate ground wire.

Transmit or transmitter - when Morse code was used, the letter X was commonly keyed rather than the full word, Tx rather than transmitter, xmit rather than transmitter xceiver rather than receiver or Rx for receive/receiver. Label for transmit line pinouts.

Universal Asynchronous Receiver Transmitter. The main component of any serial interface card. Converts serial data to/from a parallel I/O bus on a microprocessor or PC. The most popular versions include transmit and receive FIFO (First In, First Out) buffers for faster data transfers with less CPU overhead

Single-ended signal referenced to ground or common. Noise/hum picked up cannot be canceled, often requires shielding. Compare to differential or balanced outputs or inputs. In balanced signals, the outputs are 180 degrees out of phase, in-phase common mode noise is cancelled in the receiver. Example RS-232.

Un-interruptible Power Supply - a back-up power source that provides power conditioning and back-up power when the main power is lost due to electrical storms or other causes.

Universal Serial Bus - a limited range high speed serial bus standard used to expand or add functionality to a host computer. Permits connecting peripheral devices such as hard drives, printers, scanners, optical drives, real time video/audio devices or legacy serial or printer ports.

Requires drivers for the host Operating System or requires that the OS provide compatible drivers as part of the system software. Separate drivers usually required for MacOS or Windows OS.

- used for upstream connection toward host

- used for upstream connection toward host

- used for downstream connection toward device(s)

- used for downstream connection toward device

(Unshielded Twisted Pair) Connector - See RJ-45

Volts AC - AC is Alternating Current

Volts DC - DC is Direct Current

A transient, very short term high voltage on a signal or power line.

Wide Area Network

Hardware device that monitors activity with a timer. If the monitored activity ceases for longer than the time period, times out and sets off a alarm or resets the device or reboots the computer.

Usually Radio Frequency wave transmission/reception but may use Infrared wave signals.

RF modem

A multi-element antenna which is sharply more sensitive to signals in the front direction, and much less sensitive to signals at the sides and rear. Elements at the rear are longer than the active elements. Elements at the front are shorter. The size and spacing of the elements is a function of the transmitted/received wavelength (frequency), antenna gain is compared to a dipole (3dB) or omni (0dB). Increased numbers of elements makes the antenna more directional and provides more gain in the front direction. The Radiation Pattern is Heart shaped with the tip of the heart toward the short end, may be vertical or horizontally polarized.