From: gerg@netcom.com (Greg Andrews)
Subject: Re: Worldblazer not autobauding correctly at 38400
Followup-To: comp.dcom.modems
Summary: That's not autobaud
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date: Sat, 19 Dec 1992 09:17:53 GMT

brad@clarinet.com (Brad Templeton) writes:
>
>I have a worldblazer, and I set it up with S51=253, which is the autobaud
>setting with default to 38400.
>
>I also like to set up my modems in non-locked interface speed mode, so
>that incoming non-error correcting modem calls talk at the speed of the
>protocol, and users have to use getty to set their baud rate.
>
 [...]
>
>Anyway, this should be the way of it, but it doesn't seem to work on the
>WB.  When calls come in in PEP mode or v.32/v.42bis mode, for example,
>sometimes the modem interfaces at 38400 and sometimes it does it at 19200.
>There seems no way to predict this.
>
>Anybody know about this problem?
>

Yes.  It's most often a combination of two events:  (1)  The modem doesn't
have &D3 set as it should, or (2) something in the computer is sending
an AT command at 19200.

S51=253 is "autobaud, default to 38400", but only if the modem is in
the autobaud state.  That is, if the modem is searching for the computer's
RS232 speed.  If the modem is not searching (has locked onto a speed),
it won't default to 38400 unless that happens to be the speed of the AT
command the modem locked onto.

You see, S51=255, S51=254, and S51=253 are unique modes.  The modem performs
autobaud, but only on the FIRST AT command.  Once the modem senses the speed
of that first command, the modem STAYS AT THAT SPEED.  It's no longer in
autobaud mode.  So an outbound call at 19200 would cause the modem to shift
to 19200 and stay there.  At that point, the modem will use 19200 bps for 
inbound calls also - that's the computer's last known speed.

The modem will return to the autobaud state on certain events:

	o Reset by turning power off and back on, ATZ command, or drop
	  of DTR when &D3 is set (and stored configuration has an autobaud
	  setting of S51, naturally).

	o S51 register is set to the value 252-255.

	o A break signal is received from the computer.


The usual method for Unix systems is setting &D3 so the modem returns
to the state spelled out by the stored S51 setting.  If 253, autobaud
defaulting to 38400 for incoming calls.

Once you have that configured, you need to make sure nothing, absolutely
NOTHING in your computer plays with the modem's S51 and &D settings (which
includes issuing commands like AT&F and ATZ).  You'll also need to make
sure the computer drops DTR when the call is disconnected.

>
>I guess the ideal system is a getty which understands the CONNECT
>messages somehow, reading modulation, error correction, and compression
>and deciding the right maximum interface speed.  But it's hard to
>make such a beast which also doesn't interfere with outgoing calls on the
>line.
>

It's not necessary to read the whole kit and kaboodle.  Just set X4,
X11, or X12 and the modem will give you the correct port speed in the
"CONNECT xxxx" message.

Question:  Does your computer support 14400 bps?  That's the speed of a
V.32bis connection without error control when you have the speed unlocked
(S181=0).  If your system can't support that, you'll probably have to
go to a locked speed anyway...

-- 
:::::::::::::::::::  Greg Andrews  gerg@netcom.com  :::::::::::::::::::
ObGuindon:  "The way the economy works, if a man has ten carp
            and he gives four to the government, no matter how
            you slice it, he's still stuck with six carp."
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Newsgroups: biz.comp.telebit