Re: [patch] DTR/DSR hardware handshake support for 2.0/2.2/2.4

From: Martin Schenk (
Date: Wed Aug 02 2000 - 09:17:02 EST

DTR/DSR is a very often used handshake for serial printers, at least
in the POS field. A lot of supermarket cash registers are in fact PCs
with special hardware, which for some unclear reason typically knows
only about DTR/DSR handshaking (even if it is from other vendors:
SNI or EPSON does not make a difference: only DTR/DSR).

Sending people to a thousand stores around the country putting special
cables between printers and computers is simply not acceptable (if you
know POS service people, you know that about half of the cables would
be put on the wrong serial ports).

This patch is very small and you should be able to easily see any side
effects it might have.

hope you change your mind,


Theodore Ts'o wrote:
> Date: Tue, 01 Aug 2000 18:35:22 +0200
> From: Martin Schenk <>
> As I needed support for DTR/DSR hardware handshake to communicate with
> a serial printer (and the "wire RTS/CTS to DTR/DSR" tip from the
> serial-HOWTO works fine for a demo, but is not applicable for a few
> thousand POS terminals *gg*), I implemented this functionality.
> Yilch. This is specialized enough that I'd much rather this *not* go
> into the kernel. Next thing we know, someone will want a DTR/CD
> handshaking mechanism, etc.,etc.
> This should probably be a private kernel patch, or (much more strongly
> suggested) that you just get specially wired RS-232 cables. This is in
> fact a very standard thing to do, and you can order cables from Black
> Box or some other company specializing selling cables which connect
> crufty legacy hardware.
> - Ted
> -
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