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In article <539@vice2utc.chalmers.se>, d5kwedb@hacke9.dtek.chalmers.se.
(Kristian Wedberg) writes:
> I've written a Videotex program (Prestel type) for the Amiga, a kind of
> communication program. Trouble is, here in Sweden some folks have 75/1200
> modems instead of the more normal 1200/1200. 
> 
> As it is, I have no idea how to support 75/1200, or indeed, if it's at all
> possible.
> 
> Altzo, is it possible to transmit 75 bit/s and receive 1200 bit/s over
> the serial port? At the same time? Or would you need some kind of transformer?
> 
> 	wonders kitte				d5kwedb@dtek.chalmers.se

Hi there,

You will find it exceedingly difficult, if not impossible, to support
75/1200 directly on the Amiga, because the Amiga does not support split
baud rates. 1200/75 on the other hand (as might be offered by a comms
package) is much easier. I wrote a routine to do just that (i.e. send at
75 baud, receive at 1200 baud) for use with the Compunet Terminal software
(Compunet is a Commodore/Atari Quantum-Link type system in the UK), to allow
people to use the cheap "dumb" modems available in the UK to access Compunet.

It works by expanding each character to be sent at 75 baud into 16 characters
which are transmitted at 1200 baud, the 16 characters being chosen to produce
as close a copy as possible of the desired 75 baud signal. It works pretty
well, and it doesn't need to access the serial hardware directly (unlike some
other methods I've seen). It should also work with any other computer that can
send consecutive bytes over the serial line with no delay.

I have a 12K file describing the theory, and giving example C code to show
how it's used. I'm about to mail it to you, but if anyone else is interested
(the reason for this reply) send me some mail to get a copy.

       -- Eddy
-- 
Eddy Carroll               ----* Genuine MUD Wizard  | "You haven't lived until
INTER: ecarroll@cs.tcd.ie                            |    you've died in MUD!"
 UUCP: {..uunet}!mcvax!ukc!cs.tcd.ie!csvax1!ecarroll |  -- Richard Bartle