Advantech 4-Port RS-232 Interface card PCL-849 - Manual (Page 26)

Chapter 4 Wiring 27
Wiring
RS-232 signal wiring
Since the RS-232 interface is not strictly defined, many devices have
their own connection methods which may ignore some signal lines or
define reserved lines for other functions. It is best to refer to the user’s
manual for your device for installation instructions. You may find the
following helpful.
In general, DTE (Data Terminal Equipment) refers to the device that
is leading the communication. Examples include PC’s, terminals and
some printers. DCE refers to the device being communicated with or
controlled. Examples include modems, DSU’s (digital service units),
printers and lab/factory equipment.
In some situations you may be able to get by with just three lines: data
on TXD, a signal ground and a handshaking line. Examples are printer
or plotter connections, troubleshooting and situations where you
require only one-wire communication.
Terminal or PC (DTE) connections
DB-25 Male: PCL-849 DB-25 Male or Female:
Terminal
Pin Signal Pin Signal
2 TxD 3 RxD
3 RxD 2 TxD
4 RTS 5 CTS
5 CTS 4 RTS
6 DSR 20 DTR
7 GND 7 GND
20 DTR 6 DSR
8 DCD 8 DCD