Not all NULL modem cables are alike. Many null modem cables do little more than trick your computer into thinking all the appropriate signals are present (and then swap transmit and receive data). This is ok, but it means that you must use software flow control (XON/XOFF) that is less efficient than hardware flow control. The following cable provides the best possible signalling between machines, and it allows you to use hardware (RTS/CTS) flow control.
Pin Name Pin Pin
Tx Data 2 ----------------------------- 3
Rx Data 3 ----------------------------- 2
RTS 4 ----------------------------- 5
CTS 5 ----------------------------- 4
Ground 7 ----------------------------- 7
DTR 20 -\--------------------------- 8
DSR 6 -/
RLSD/DCD 8 ---------------------------/- 20
\- 6
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