2400 BAUD MODEM COMPATIBILITY

I recently purchased a 1/2 card 2400 baud modem to use on my BBS. I
ordered it from a company that advertises in that 'classified ad' magazine,
it was only $239.

After receiving and installing the 'Smalltalk' modem I noticed that it
answered the phone with only one tone, some of the other 2400 BBS's in town
answer with 2 tones. The modem seemed to be compatible in every way with
the Hayes including the non-volatile RAM and most callers could connect up
and operate without any trouble. There were a couple of people in town
that could not connect at 2400 baud, and after doing further research found
that their modems could not connect to any modems that did not produce the
two tone answer.

After still more research and testing I discovered that the single
answer tone is CCITT format (ATB=0) and the two tone answer is BELL format
(ATB=1). There is apparently no difference to 300/1200 baud callers in the
two modes and most 2400 baud modems will connect up with the BBS modem in
either mode. But Leading Edge modems (and maybe others) will connect up
only to those modems using the BELL format answer.

The Hayes manual is even a bit confused on the difference in one place
it says BELL is the default, in another it says CCITT is. But if you give
it the AT&F&W command to rewrite the factory settings the result of ATB?
will be 1 (BELL).

To set up any Hayes compatibles to run this format on a BBS bring up a
modem program and issue the following commands: AT&F&W (sets to factory
defaults) AT&C1&D2&T5E1&W (sets the modem to allow DTR control, true
carrier detect, prevent callers from starting test, and make no echo the
default the &W writes the new values out). These will be the values
restored when an ATZ is executed.

To setup for BELL compatibility type: ATB? (if it returns 000 then it
needs to be changed), ATB=1 (to set for BELL) ATB? (should now report 001)
AT&W to write this into the default. An ATM1A should now produce the
needed 2 tones.

Does anyone have an explanation for this two tone format? Is it to
help the modems sync up better at 2400 baud?

Thanks, Dennis Wynne
Troll's Cave BBS (615)242-7909