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From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.sys.sgi
Subject: Re: Any handshake in any port.
Message-ID: <67712@sgi.sgi.com>
Date: 26 Aug 90 06:01:25 GMT
References: <9008260014.AA17061@mcirps2.med.nyu.edu>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 33


Each IRIX tty port has three aliases, distinquished by the two most
significant bits of the minor device number, or by the /dev/tty[dmf]* name.

ttyd* use pins 2,3, & 7.  Thus, the system simply babbles the output, 
    subject at most to XON/XOFF flow control.  At high speeds, either the
    system or the printer will loose ^S or ^Q characters and bad things
    will happen.

ttym* use 2,3,7,8, and 9/20.  The system will refuse to complete an open(2)
    until pin 8, DCD, is true.  Otherwise, ttym* are the same as ttyd*.  A
    handy hack is to connect pins 8 and 9/20, to make a ttym* that is
    really connected to a dumb, 3-wire device complete an open(2).

ttyf* use 2,3,4,5,7,8, and 9/20.  A port under its ttyf name behaves the
    same as under its ttym name, except that it honors CTS as required by
    RS-232-C, and expects the device honor RTS as in the de facto standard
    "hardware flowcontrol".

Thus, to use "hardware flowcontrol" on an otherwise dump printer, use a
cable with 2,3,4,5, and 7 connecte to the printer and 8 jumpered to 9/20
on the IRIS, and use the ttyf name.

Restrictions in the way STREAMS work make it impossible to open a single
port under more than one of its aliases at a time.  That is, if you already
have ttyd3 open, you will not be able to open ttyf3.

All current IRISs support all three types of tty[dmf]* names on all
integral DUART ports and all of the up to 32 CDSIO ports.


Vernon Schryver
vjs@sgi.com