Electrical specification
32
The RS232 port is a standard 9-pin D plug. The functions DSR,
CD, and RTS are connected together within the 1902 case so
that a simple pin-to-pin cable can be used. The RS232 serial-
line cable provided with the 1902 has a 9-way D-type socket at
each end, suitable for AT and ATX chassis PCs. The baud rate
is fixed at 9600.
Pin Function Wire colour
5 Signal ground
4 DTR to 1902
3 Data to 1902
2 Data from 1902
1 CD
6 DSR
7 RTS
8 CTS from 1902
9 No connection
Shell Cable screen
• For correct EMC performance it is essential that the serial-
line cable connectors have good-quality metal shrouds, and
that they are clamped with integral jackscrews to the
threaded posts provided on the 1902 and on the computer
• The cable must be screened with metal braid or foil, which
should be clamped to the shrouds at both ends
To use the 1902 with a computer such as a laptop that may not
have a physical com port, consider one of the commercially-
available devices that implement a virtual RS232 port on the
end of a USB plug. The special RS232 cable supplied by CED
must still be used. See page 13 for more on this.
RS232 port
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