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With DB25 connectors, usually (?):
DCE is female (modem)
DTE is male (PC com port)
DB9 on PC and AT: male
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RS-232 definitions:
DB-25 DB-9
DTE DCE DTE DCE
Protective Ground PG 1 1
Transmit Data TD 2 3 3
Receive Data RD 3 2 2
Request To Send RTS 4 5 7
Clear To Send CTS 5 4 8
Data Set Ready DSR 6 20 6
Signal Ground SG 7 7 5
Carrier Detect CD 8 8 1
Data Terminal Ready DTR 20 6 4
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PC Com1: Com2:
IO ports 3F8-3FF 2F8-2FF
IRQ 4 3
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BB Electronics 232-422 converters:
model 422COR has a female DB25 on the 232 side, to plug
directly into the male DB25 DTE port of a PC: That is,
it is wired as a DCE, like a modem.
PG 1
TD 3
RD 2
RTS 5 _
CTS 4 _|
DSR 20 ___
SG 7 |
CD 8 ___|
DTR 6 ___|
On the RS422 side, the male DB25 has:
TDA(-) 2
TDB(+) 14
RDA(-) 5
RDB(+) 17
gnd 7
12V + 25
12V gnd 12
signs indicate polarity with no data.
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