55
MODULAR SMART SWITCH
Figure A-1. IBM PC/XT Serial Cable Pinning.
If you already have a cable that works directly between your IBM PC and
serial printer, it may be suitable for use as the input cable to your Modular
Smart Switch.
A.2.2 RS-232 C
ONNECTIONS TO
IBM AT
AND
C
OMPATIBLES
The IBM AT and compatibles provide a DB9 connector for the serial port.
The cable required to connect to the Modular Smart Switch is wired as shown
in
Figure A-2
.
2
3
5
6
7
IBM PC end
25-Pin socket connector
3
2
7
5
Modular Smart Switch end
25-Pin socket connector
RXD
TXD
DTR
GND
CTS
4
20
54
MODULAR SMART SWITCH
Table A-1 (continued). DB25 Serial Pinouts.
Pin
Description
RS-232
RS-422
In/Out
10
Flow control out (+ve)—hardware
HSOUT + Output
handshake
11
Received data (-ve)
RXD -
Input
12
Received data (+ve)
RXD +
Input
13
Transmit data (-ve)
TXD -
Output
15
Flow control in (-ve)—hardware
HSIN -
Input
handshake
16
Flow control in (+ve)—hardware
HSIN +
Input
handshake
25
Transmit data (+ve)
TXD +
Output
A.2 Connecting to Computers—RS-232 Connections
RS-232 serial ports on computers tend to vary considerably. The standard
recommends a DB25 connector, but some machines, such as the IBM AT and
compatibles, use a DB9 connector. Computer ports intended for connection
to a modem are not configured like those intended for connection to a serial
printer. Because of all these variables, a “standard” RS-232 cable does not
exist.
NOTE
You might need to refer to the documentation supplied with your
computer to establish the type of cable required. The following
specifications may help you decide on the required cable.
A.2.1 RS-232 C
ONNECTIONS TO
IBM PC
S AND
C
OMPATIBLES
The IBM PC and its compatibles provide a parallel port and (usually) an RS-
232 serial port. Both use a DB25 connector. However, the parallel port is
normally a socket (female) connector, and the serial port is normally a plug
(male) connector. The cable wiring required for connection to a serial port
on the Modular Smart Switch is shown in
Figure A-1
.