software null modems
David W. Hess
dwhess at banishedsouls.org
Sat May 17 14:10:11 UTC 2008
On Thu, 15 May 2008 09:19:49 -0400, "Aryeh M. Friedman" <aryeh.friedman at gmail.com> wrote:
>I need a null modem and all I can find is straight through db25 cables
>and I want to avoid the paper clip trick if I can. So is there any way
>to create a null modem in software only?
Unless you have some really unusual hardware on at least one side, this will not be
possible. With rare exceptions that occasionally show up in embedded systems, hardware
UARTs all have fixed function I/O pins. This is even more the case with RS-232 (or
RS-422) because signal level translation from and to logic levels is needed.
It is not difficult to modify an existing cable as long as you do not need hardware flow
control. Just swap pins 2 and 3.
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