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1990-11-05
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APPENDIX F -- RBBS-PC And The AT's RS-232 Cable F-1
APPENDIX F -- RBBS-PC And The AT's RS-232 Cable
-----------------------------------------------
The RS-232 serial connector is different for the AT than the PC or XT. The
AT uses a connector called a DB-9, which is a 9 pin connector. An
alternative to buying the AT serial cable from IBM, ($65-$80), is to make
your own. A ten-wire cable can be purchased from any local computer store
for about $.80 per foot, and the DB-9 and RS-232 connectors with hoods can
be purchased from Radio Shack. The total cost should be about $12.00. A
modem hooked up to the AT will work fine with the 9 pins connected in all
terminal functions, except for auto-answer applications such as RBBS-PC.
RBBS-PC requires pin 1 from the modem to be hooked up to the chassis ground
on the AT or it can't answer the phone. There are two ways to hook up the
ground wire on the computer end. The first way is to use a metal hood to
cover the DB-9 connector. Wrap a bare wire that is attached to pin 1 of
the RS-232 connector around the cable on the DB-9 end. When the metal hood
is screwed down over the cable a connection will be made. When using a
plastic DB-9 hood simply solder a wire from pin 1 on the RS-232 end to the
metal body of the DB-9 connector. Since documentation is scarce for the
AT, following figure lists the necessary pin connections for those wanting
to make their own AT RS-232 cable.
DB-9 RS-230
(Computer (Modem Description
End) End)
========= ======= ==================
GROUND -------- 1 -------- Protective Ground
1 -------- 8 -------- Data Carrier Detect
2 -------- 3 -------- Receive Data
3 -------- 2 -------- Transmit Data
4 ------- 20 -------- Data Terminal Ready
5 -------- 7 -------- Signal Ground
6 -------- 6 -------- Data Set Ready
7 -------- 4 -------- Request to Send
8 -------- 5 -------- Clear to Send
9 ------- 22 -------- Ring Indicator