ASCII TTY's were usually 110 baud. This gave them 10 CPS bacause they used
an 11 bit word (2 stop bits). They used current loop and required a
hard-copper connection from one end to the other.

When modems came out, which allowed transmission over normal AC coupled
phone lines, they started at 300 baud (30 CPS with one stop bit), exactly 3
times faster.

As modems improved they always seemed to stick to powers of 2 improvement
over that (with a few exceptions like the 75/150 BPS back channel in teletex
and Bell 202).

The 'really high rates' like 57,600 and 115,200 are small integer multiples
of 19,200, which is 2^6 * 300.

There were some funny cases like 1800 and 3600 baud thrown in to fill in the
gaps.

For a really wierd rate try the one used by terminals based on the IBM
selectric mechanism: 134.5 baud. This had to be related to the physical
speed of the existing typewriter mechanism.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
sofftware)


----- Original Message -----
From: Phillip Vogel <phillip@BARTAL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, August 16, 2000 10:25 AM
Subject: Re: [PIC]: MIDI input and audible output


> Andrew Kunz wrote:
> >
> > I've always considered the standard RS232 rates crazy because they were
not
> > powers of 2 nor multiples (divisors?) of even MHz rates (such as  4MHz).
> >
> > Andy
> >
>
> Agreed. Again, this all probably has to do with some horse's ass somewhere
> back in time... Then there were the old teletypes, at 110 or (i think)
113.5.
> Sheesh, If those guys who thought that stuff up had had a time machine,
they
> could have looked about 80 years into the future and seen what a mess they
> were setting us up for.
>
> However, those crazy speeds like 38.4K are very firmly established, like
it or
> not, we have to live with them. They were also firmly established long
before
> the birth of MIDI. There have been times when I would have liked to have
been
> able to use a PC serial port to do midi, without any rate conversion...
>
> The nice thing about standards is that there are so many to choose from.
>
> P.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.

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