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Appendix A: Serial Ports
A.1 RS-232 and RS-422 Pin Assignments
The serial ports on the Modular Smart Switch use DB25 connectors. The
following table lists RS-232 and RS-422 pin assignments and signal
descriptions. Those pins not appearing in the table are not used.
Table A-1. DB25 Serial Pinouts.
Pin Description RS-232 RS-422 In/Out
1 Protective ground (shield) EARTH EARTH —
2 Transmitted data (data out) TXD Output
3 Received data RXD Input
4 Request to send—Always held HIGH RTS Output
5 Clear to send—flow control in CTS Input
(hardware handshake)
7 Signal ground GND —
20 Data terminal ready—flow control out DTR Output
(hardware handshake)
9 Flow control out (-ve)—hardware HSOUT - Output
handshake
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10.7 Merged Printouts
If the output from one computer has been printed in the middle of that from
another, you will probably need to increase the timeout period. When no
data has been sent from one computer for the timeout period (by default
16 seconds), the Modular Smart Switch will allow another computer to start
printing. To change the timeout period, use the control software (see Section
6.10.2) or send a software command (see Section 9.2.4). The default timeout
period is set using the option switches on the main board (see Section 4.1).
10.8 Print Data Transmitted but File Transfer Fails
If you can print normally using your PC’s serial port but file transfer fails,
check the following:
• Make sure that the control software is installed.
• Make sure that the protocol is set to 8 bits, 1 stop bit, no parity.
• For hardware handshake, make sure that pins 4 and 5 are connected
on the Modular Smart Switch end of the computer serial cable.
