Re: IIGS 115,200 Baud Serial Port - How?

[Hugh Hood <hughhood@earthlink.net>]

David,

Actually, I meant the _1X_ clock factor.

At _32X_, with the Baud Rate Generator enabled, _no_ values for the Time
Constant will produce a 115,200 baud rate, because as you previously
demonstrated (I listened to you then, and I believe you now <g>), the
denominator of the formula becomes too high to be overcome by a Time
Constant integer > 1.

Now, however, with your detailed explanation of why a 1X clock factor is not
functional in our particular application, I understand why I obtained such
unsatisfactory (to say the least) results using 1X. Thanks for going into it
for me.

Gary Little is an amazing guy. I own (and refer to) a couple of his books,
and still remember his time as an editor of A+ Magazine.

I recall reading in the old Open-Apple magazine that Little's training was
as an attorney. Man, I'm glad he turned his life around!

Correct me if I'm wrong, but I think development on Point-to-Point stopped
before Little had a chance to add the Zmodem protocol. That, however, should
not be relevant when you start your patching for 115,200 baud.

Thanks again for the input on serial comm. I appreciate it.

Hugh Hood...



in article 
b2f516cf-9183-47ce-9cca-5ae2c02bde6f@z28g2000prd.googlegroups.com, David
Wilson at mcs6502@gmail.com wrote on 1/1/09 5:11 PM:

> On Jan 2, 5:55�am, Hugh Hood <hughh...@earthlink.net> wrote:
>> I recalculated the time constants
>> for a _1X_ clock factor (please disregard my previous post showing my
>> calculated time constants -- way off) , patched those in, re-enabled the
>> Baud Rate Generator, set the clock factor to 1X, and tried again.
> 
> I hope you really mean _32X_ rather than _1X_ because standard async
> comms using NRZ encoding cannot use the _1X_ setting. The reason is
> that you need to sample the incoming bit stream near the centre of
> each bit. The way an ACIA/UART works is by using a 16x/32x/64x clock
> and counting 8/16/32 periods after the leading edge of the start bit,
> checking that the start bit is still present (false start bit
> detection) and then sampling every 16/32/64 periods for each bit that
> follows.
> 
> I don't have ProTerm but I do have Gary B. Little's PointToPoint which
> I believe I can add a new serial port module to. Should be interesting.