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Home > Tech Notes > Pinout and COM Port Summary Card

Pinout and COM Port Summary Card

EIA-232-E (RS-232)
Function

PIN #
DB-25	DB-9

EIA-530
Function

PIN #
DB-25

TO
DTE

TO
DCE

Shield

Transmit Data (TD)

Transmit Data	(A)
	(B)

2
14

Receive Data (RD)

Receive Data	(A)
	(B)

3
16

Request To Send (RTS)

Request To Send	(A)
	(B)

4
19

Clear To Send (CTS)

Clear To Send	(A)
	(B)

5
13

DCE Ready (DSR)

DCE Ready	(A)
	(B)

6
22

Signal Ground (SG)

Signal Ground

(A)

Received Line Signal Detector (DCD)

Received Line Signal Detector	(A)
	(B)

8
10

DTE Ready (DTR)

DTE Ready	(A)
	(B)

20
23

Ring Indicator

N/A

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SIGNAL STATE	THRESHOLD VOLTAGES
	Signal with Respect to SG	Signal A with Respect to Signal B	Signal A with Respect to Signal B
	RS-232	RS-422	RS-485
"0", Asserted, ON, Space, Active	+3 to +25 VDC	+2 to +6 VDC (Transmitter) +0.2 to +7 VDC (Receiver)	+1.5 to +6 VDC (Transmitter) +0.2 to +12 VDC (Receiver)
"1", Disasserted, OFF, Mark, Inactive	-3 to -25 VDC	-2 to -6 VDC (Transmitter) -0.2 to -7 VDC (Receiver)	-1.5 to -6 VDC (Transmitter) -0.2 to -7 VDC (Receiver)
NOTE: Some RS-422 and RS-485 equipment use "+" and "-" descriptors. The "-" corresponds to "A" and the "+" corresponds to "B".

Common AT Port Addresses and Interrupts
COM 1	3F8h	IRQ4
COM 2	2F8h	IRQ3
COM 3	3E8h	IRQ4
COM 4	2E8h	IRQ3
LPT1	378h	IRQ7
LPT2	278h	IRQ5
LPT3	3BCh
Floppy Disk		IRQ6
Real Time Clock		IRQ8
Re-directed to IRQ2		IRQ9
Math Co-processor		IRQ13
Hard Disk		IRQ14