.TH RS-232 "" "" "Technical Information"
.PC "Serial port wiring"
.PP
.II "modem^cabling"
.II "terminal^cabling"
.II "printer^cabling, serial
.II "DB-9P connector"
.II "DB-25 connector"
.II "connector^RS-232C"
.II "connector^DB-9P"
.II "connector^serial"
.II "serial port"
.II "port^serial"
.II "pinout^RS-232"
.II "pinout^DB-9P"
This article details the connections (pinouts) of EIA standard RS-232C.
This connector consists of a D-shaped plug with 25 pins in two rows:
13 pins in the upper row and 12 in the lower.
This interface is commonly used by devices that require a serial
interface to a computer; these devices
include modems, terminals, serial printers, and such specialized
devices as bar-code scanners.
In addition, this articles gives the pinouts of the nine-pin DB-9P connector,
which is a nine-pin version of the RS-232 that is commonly used in AT and
AT-compatible computers.
.SH "RS-232 Pinout"
The following table gives the 25-pin EIA standard RS-232C pinouts.
It also gives:
.DS
	\(bu	Nine-pin DB-9P convention
	\(bu	Common abbreviations of signal names
	\(bu	Abbreviations of RS-232 signal names
	\(bu	Equivalent CCITT signal-number designations
	\(bu	Signal direction (as appropriate)
	\(bu	Signal description
.DE
.PP
.II DTE
.II DCE
Please note that in this table,
.B DTE
stands for \*(QLdata terminal equipment\*(QR and refers to
terminal-type equipment such as a PC or a terminal, whereas
.B DCE
stands for \*(QLdata communications equipment\*(QR
and refers to modems and modem-type equipment.
.sp \n(pDu
.nf
.ta 0.01i 0.55i 1.1i 1.8i 2.15i 2.7i 3.5i
	\fIDB-25	DB-9	Common\fP
	\fIPin #	Pin #	Name	EIA	CCITT	DTE-DCE	Description\fP
.ta 0.2i 0.7i 1.2i 1.8i 2.25i 2.9i 3.5i
	1		FG	AA	101	\(em	Frame ground
	2	3	TD	BA	103	\(->	Transmitted data
	3	2	RD	BB	104	\(<-	Received data
	4	7	RTS	CA	105	\(->	Request to send
	5	8	CTS	CB	106	\(<-	Clear to send
	6	6	DSR	CC	107	\(<-	Data set ready
	7	5	SG	AB	102	\(em	Signal ground
	8	1	DCD	CF	109	\(<-	Data carrier detect
	9		\(em	\(em	\(em	\(em	Positive DC test voltage
	10		\(em	\(em	\(em	\(em	Negative DC test voltage
	11		QM	\(em	\(em	\(<-	Equalizer mode
	12		SDCD	SCF	122	\(<-	Secondary carrier detect
	13		SCTS	SCB	121	\(<-	Secondary clear to send
	14		STD	SBA	118	\(->	Secondary transmitted data
	15		TC	DB	114	\(<-	Transmitter clock
	16		SRD	SBB	119	\(<-	Secondary receiver clock
	17		RC	DD	115	\(->	Receiver clock
	18		DCR	\(em	\(em	\(<-	Divided clock receiver
	19		SRTS	SCA	120	\(->	Secondary request to send
	20	4	DTR	CD	108.2	\(->	Data terminal ready
	21		SQ	CG	110	\(<-	Signal quality
	22	9	RI	CE	125	\(<-	Ring indicator
	23		\(em	CH	111	\(->	Data rate selector
	24		TC	DA	113	\(<-	Transmitted clock
	25
.fi
.SH "Files"
\fB/usr/pub/rs232\fP \(em On-line version of above table
.SH "See Also"
.Xr "Administering COHERENT," administe
.Xr "asy," asy
.Xr "modem," modem
.Xr "terminal" terminal
.br
Seyer, M.D.:
\fIRS-232 Made Easy: Connecting Computers, Printers, Terminals, and Modems\fR.
Englewood Cliffs, NJ, Prentice-Hall Inc., 1984.
.SH Notes
Serial ports on the back of the PC use either a 25-pin male (DB-25P)
or a nine-pin male (DB-9P) connector.
.II "stupidity, IBM"
Due to what can only be regarded as extreme stupidity, the 25-pin
female (DB-25S) connector was chosen for the parallel (printer) port,
rather than using the usual 36-pin parallel connector.
Do not confuse these ports when wiring custom-cable assemblies, as you
can damage your equipment!
