SUMMARY: 14400 Baud Modem

From: David Paul McLaughlin (
Date: Sat Jan 09 1993 - 17:18:56 CST

My original posting:
>I'm running SUNOS 4.1.3 on a Sparc2 (and Viking) machine.
>I have a ZyXEL U-1496 series modem that can run at 14400 bps.
>I can't seem to run tip, cu, or any program that sets the tty
>to that baud rate.
>Has anyone done this?
>Your help is greatly appreciated!

A key seems to be that the modem to computer communication rate
can be different, in fact should be higher like 19200, than the modem to
modem rate.

Sorry for the delay in sending this summary, but I have not
as yet been able to get my modem to work using a getty.
I was, however, able to get it to work using a program
I wrote that manualy sets the baud rate to 38400 (had touble with 19200).
This hack work for what I needed because I could the run slip.
I just haven't had time to mess with the modem lately and probably won't for
a while, so I'm posting all the responses I received in full.

Special Thanks to all who replyed! These are their replies: (Brett Lymn)
Normally modern modems will accept a different DTE speed to that they
are transmitting at, try talking to the modem at 19.2K.

David Fetrow <>
Have you tried 9600 and 19200? The modem should compensate at its end
as appropriate. I don't have the setup strings we used handy here though.
GoodLuck. (Brian Keves)
That is the modem to modem rate. You set the DTE rate at whatever you need to
to properly talk to the modem from your computer.

If you setup your connection with hardware flow control then Sun only
guarantees 19200 bps, but you can probably go up to 38400 bps ok.

You want as high a transfer rate as possible since the ZyXel runs
V42.bis if you want it to, which gives you compression and a much higher
throughput than 14400 bps. (Michael G. Harrington)
My understanding is (and of course this might be wrong!) is that in order to get to
14400 baud, you must run the modem at 9600 and enable compression (V32.bis) which
will effectively send it to 14400 baud. If you enable V42.bis, 4 times the speed
is possible.

The only thing I know is that I run my 14400 (intel) modems at 9600, enable compression
and everything is fine. (David Sharp)
If your ZyXEL is anything like the Boca 14400 that I've used, you should
use the modem at 19200 baud (or faster) at your serial port. The modem will
then communicate fine with other systems at 14.4k baud. (Todd L. Kindig @ Micom Comm. Corp.)
I have my sparc and ZyXEL running just fine using kermit.... I
set the baud rate to 38400 (the fastest the Sun seems to be able
to go) and let the modem do the rest.... I don't have my S
register settings handy, but if I recall right, the only one I
had to change had to do with dial in access, not dial out....

"Patrick M. Landry" <>
14400 is the baud rate between the two modems. You can communicate
with the modem at whatever speed you like and the modem will handle
the switch. I run mine at 19200 or 38400.

James J Dempsey <>
Just set the tty to be 19,200 (or even higher) and use hardware
handshaking between the modem and the SS2. Since the ZyXEL will run
at 14,400bps but also has V.42bis compression, effective transfer rate
can be higher than 19,200 sometimes. If you use hardware handshaking,
then you never have to worry that the SS2 will outrun the modem or
vice versa.

I have a USR sportster 14,400 that I run at 19,200 on my HP 9000/720
and a USR courier that I used to run at 19,200 on my SS2.

Configure your /etc/remote file to have an entry
that supports 14400 baud; then you can use
any of the standard modem programs. (Matt Goheen)
Normally, you set the DTE/DCE rate higher than the data rate and set the modem
up to allow this. How you do this depends on the modem, but it is usually
called something like "lock DTE rate" or some such. On our Codex modem, it's
simply AT*DExx to set the DTE rate (where xx is a value that corresponds to
some baud rate, i.e. 15 is 38.4Kbuad). On our PP FDX9696, you use AT&B1 to
"Freeze DTE rate". This is a little tricky because you must connect to the
modem at the rate you need and let it autobaud to your rate, then do a AT&B1&W
to save the configuration.

Many people seem to think that the data rate and DTE/DCE rate must match. That
hasn't been true for several years and in fact doesn't work when you throw
data compression (v.42bis or MNP5) in... (Russ Poffenberger)
14.4K is not a typicical baud rate. It is the modem data rate for v.32bis.

Use 19200, or even 38400 baud and let the modems to the baud rate translation. (Dirk Behrens)
Sorry to answer with a question.

But I 'm trying to set up a ZyXEL U-1496 on my SPARC 2 but it doesn't work well.Which file(s) do you have edited and what are your modem settings ?
I done all written in the answerbook about connecting a modem. I still can use
kermit to set AT commands and the modem answers when I call it, but on the calling screen appeares only hirographic characters. I tried all the various modes:
8 bit, 7 bit, each parity type and so on. But ....

mrt!mike@suntan.West.Sun.COM (Mike Flynn)
Normally a modem will interface to a SUN port at 9600 or 19200 while
communicating over the phone line at 14400 or what ever rate it can.
Occassionally a rate is required that is not one directly available
in UNIX.

As a software engineer for MAGMA having writen device drivers for MAGMA
and SUN boards I have devised a way to set MAGMA ports to any bps rate
including the 14400 bps required by some hispeed modems. MAGMA ports
be forced to support combinations that UNIX (SUNOS) does not support.
The OS can see the port at any of the standard rates while
to port can operate at any rate form 40 to 115200 bps. Give me a call
and I can give you specific information on how this works after I learn
more about your modem installation.

Normally, your would set the terminal speed to either 19600 or 38400 and use
some kind of compression feature with the modem. (i.e. MNP5). The speed of
the link between modems is 14400 bps. This relies on out-of-band flow
control (RTS/CTS) to really work effectively. As far as I know, Suns device
driver does NOT support RTS/CTS flow control - it only supports the device
(modem in this case) controlling flow from the Sun - the Sun cannot tell the
modem to stop/start.

ups!upstage!glenn@fourx.Aus.Sun.COM (Glenn Satchell)
I don't think 14400 is one of the baud rates that the serial driver
supports. I have a 14400 baud modem here and I just access it at the
next highest rate - 19200 or 38400 - it converts this to 14400 and
squirts it down the phone line. Can your modem do that also?
   Set your port for 19200 or 38400 baud, and tell the modem to lock the
DTE speed (can't say for sure how on the Zyxel). 14400 baud, is not a
standard speed on most UARTs. (Milton Choo)
Hm, maybe you should look at the eeprom,

try eeprom | grep tty

and see the setting. Hope this help.

trdlnk!mike@uunet.UU.NET (Michael Sullivan)
Sun's serial ports don't support 14400 bps. Try using 19200 or 38400 (assuming
the modem supports them; all V.32bis modems I've seen do).

>From the termio(4) manual page, here are the possible baud rates you
can use:
            B50 0000001 50 baud
            B75 0000002 75 baud
            B110 0000003 110 baud
            B134 0000004 134.5 baud
            B150 0000005 150 baud
            B200 0000006 200 baud
            B300 0000007 300 baud
            B600 0000010 600 baud
            B1200 0000011 1200 baud
            B1800 0000012 1800 baud
            B2400 0000013 2400 baud
            B4800 0000014 4800 baud
            B9600 0000015 9600 baud
            B19200 0000016 19200 baud
            B38400 0000017 38400 baud

The modem to modem speed can be 14400 bps, but the possible DTE speeds
are limited to what the computer's serial port can do. For instance,
I use a DTE speed of 19200 bps for V.32bis modems here. In order for
compression to be of benefit, you need a higher DTE speed anyway.

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