Here is how to
construct your own null modem
connector:
1) Connect
TD of each end with the
RD of the other
2) Connect
CTS of each end with the
RTS of the other
2) Connect
DSR of each end with the
CD of the other
3) Connect
SG of each end with the
SG of the other
4) Connect
DTR of each end with the
DSR on the same end
5) If both ends of the connection are to be 25-pin, then also connect pin 1 (
Frame Ground) to pin 1 of the other.
Depending on whether you are using a 9-pin or 25-pin
serial connector, the
pin numbers will be different.
Here are the ones that are
essential for a null modem
connection.
A complete list can be found in the
serial port pinout node.
25-Pin 9-pin
----------------------
2 TD 3
3 RD 2
5 CTS 8
4 RTS 7
6 DSR 6
8 CD 1
7 SG 5
20 DTR 4