Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!uunet!math.fu-berlin.de!fub!geminix.in-berlin.de!gemini From: gemini@geminix.in-berlin.de (Uwe Doering) Newsgroups: comp.unix.sysv386 Subject: Re: SCO RTSFLOW (was re: Help Telebit and SCO RTS/CTS Setup) Keywords: RTS/CTS Hardware Flow Telebit RS-232 Unix 386 SCO Message-ID: Date: 6 Apr 91 15:56:07 GMT References: <5176@mjbtn.JOBSOFT.COM> <1991Apr5.230009.16835@netcom.COM> Organization: Private UNIX Site Lines: 41 gandrews@netcom.COM (Greg Andrews) writes: >In article gemini@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 -- Uwe Doering | INET : gemini@geminix.in-berlin.de Berlin |---------------------------------------------------------------- Germany | UUCP : ...!unido!fub!geminix.in-berlin.de!gemini