SCO RTSFLOW (was re: Help Telebit and SCO RTS/CTS Setup)

[Uwe Doering]

gandrews at netcom.COM (Greg Andrews) writes:

>In article <TMPP9FB at geminix.in-berlin.de> gemini at geminix.in-berlin.de (Uwe Doering) writes:
>>
>>This is a common misunderstanding of how RTSFLOW works under SCO UNIX (and
>>Xenix as well). SCO implemented a half duplex type of hardware flow
>>control, as it is described in the original RS232C standard. That is,
>>RTS signals the modem whether there are any characters in the _computer's_
>>output buffer. If there are none, RTS is low, otherwise it's high. This
>>won't work at all if the modem is configured to use full duplex hardware
>>flow control. In this mode RTS signals the modem that the computer is
>>ready to receive characters. As far as I know, there is no way to get this
>>working with the original SCO sio driver, as it isn't designed for that
>>type of handshake.
>>
>
>Then why does RTS stay high all the time at slower speeds?  If it behaved
>consistently, then the modem could simply be configured to use half duplex
>flow control (S58=1 S68=255) and be done with it.

Yes, but half duplex flow control, per definition, is only for one
direction (computer -> modem). This won't help you with receiving
data.

>Unfortunately, in my version of SCO Unix (3.2.0 according to the kernel),
>RTS stays on all the time when getty is using the B9600 or slower entries
>in /etc/gettydefs.  That violates the rules for half duplex RTS/CTS.  RTS 
>should be low while the computer is not transmitting.

One detail I remember now is that the RTS/CTSFLOW flags have a meaning
only if CLOCAL is cleared. That is, as far as I know, you can't use
these flags on a dialout line (tty1a, tty1b etc.) because it has CLOCAL
always set. And therefore RTS is always high. But I may be wrong here.
And maybe there are other strange interactions between flags in the sio
driver. I don't know.

     Uwe
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