Subject: Re: DEC vt320 terminal problem
To: Kevin P. Neal <>
From: Frederick Bruckman <>
List: netbsd-users
Date: 06/19/2001 08:38:23
On Tue, 19 Jun 2001, Kevin P. Neal wrote:

> On Mon, Jun 18, 2001 at 10:41:27PM -0400, Shannon Hendrix wrote:
> > I tried using rtscts hardware flow control, but it's not totally clear
> > to me that the terminal supports it. It didn't give errors, but it seems
> > that either shells turn this off, or the setting has no effect.
> You know, I don't think I ever got hardware flow control working right
> on my vt220 either. I think I ended up going 9600bps with jump scrolling.
> It was ... ok, I guess.

The DEC 6-pin connector has two differential pairs for RXD and TXD
(RS-422 signaling), DSR, and DTR, so it can support modem control, but
not hardware handshaking. Even if you use an adapter for one of the
other ports, I don't believe the hardware shaking pins are used, VT5xx

It does support software handshaking, sort of. The VT420 has a 254
character input buffer, which is shared between sessions. You can go
in the set-up screens and set it to send an XOFF at the 64 character
mark or at the 128 character mark. (It would do no good at all to send
an XOFF when the buffer is _already_ _full_ -- think about it.) That's
all it does. It doesn't care if it receives and XOFF, so if you type
faster than the computer than receive, you're going to have problems.
If you have two sessions, send XOFF at 64, and the computer happens to
send more than 63 characters between the time it receives the XOFF and
processes it, you're also going to see dropped characters/garbage.