Newsgroups: comp.dcom.modems
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Break definition
Message-ID: <1988Sep11.020002.10385@utzoo.uucp>
Organization: U of Toronto Zoology
References: <402@ucrmath.UUCP> <6095@galbp.LBP.HARRIS.COM>
Date: Sun, 11 Sep 88 02:00:02 GMT

In article <6095@galbp.LBP.HARRIS.COM> mhw@wittsend.UUCP (Michael H. Warfield) writes:
>>CCC is willing to correct the problem but they need to know how to handle
>>the break.  After all, there is no such thing as a break character.  What
>>must they do to send a break and what do they do when a "break" is received?
>>How do external modems do this?
>The modem per se should have little to do with a break (he simply
>holds his transmission to send a  looooonnnnnnngggggg  series  of
>zero  bits)  but  the  UART  or SIO has everything to do with it.

At 300 baud, yes.  At 2400, not so.  Higher-speed modems are *NOT* just
transmitting the RS232 signal as tones; they are actually receiving the
characters, packaging them up in odd ways (e.g. more than one bit per line
transition), and reversing the process at the other end.  This means that
the RS232 signal has to make sense (that's why fast modems have settings
for things like number of bits per character).  It also means that
break requires special attention, since it is *not* a character!  Tell
CCC to look up the V.22bis spec, which describes the signals on the wire
for a 2400-baud modem; it will tell them how to send a break over the
wire, and with luck will also tell them exactly when to send one and what
to do when they receive one.

Don't be too optimistic.  If CCC does not know this stuff already, I
wouldn't buy a modem from them if it cost $4.95.  They are incompetent.
They are not the only ones; this problem has been seen before.
-- 
NASA is into artificial        |     Henry Spencer at U of Toronto Zoology
stupidity.  - Jerry Pournelle  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu