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RS-232 Pinout

RS-232 (EIA-232-A) Function DB-25 pin # DB-9 pin #
Shield1
Transmit Data (TD) from DTE to DCE23
Receive Data (RD) from DCE to DTE32
Request to Send (RTS)47
Clear to Send (CTS)58
DCE Ready (DSR)66
Signal Ground (SG)75
Received Line Signal Detector (DCD)81
DTE Ready (DTR)204
Ring Indicator229
RS232 DB9 female connector RS232 DB25 male connector
DTE - Data Terminal Equipment (computers, terminals, PLC's, ...)
DCE - Data Communication Equipment (modems, scanners, ...)

RS-232 cable lengths

Data Rate (bps) Maximum Length (meters) Maximum Length (feet)
2400120400
480060200
960030100
192001550
384007.525
57600516
1152002.58

Common interrupt numbers and port addresses

Device Interrupt Port number
COM1IRQ 43F8h
COM2IRQ 32F8h
COM3IRQ 43E8h
COM4IRQ 32E8h
LPT1IRQ 7378h
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