[Coco] serial port problem

[Luis Antoniosi (CoCoDemus)]

Only the coco1 has the 741.

The coco2 and 3 use the SALT chip. It could be bad though. I got a coco3
with a bad SALT but it even didn't turn on because the SALT chip also does
the +5V regulation.



On Thu, Oct 31, 2013 at 4:45 PM, Tormod Volden <lists.tormod at gmail.com>wrote:

> On Thu, Oct 31, 2013 at 5:35 AM, Mathieu Bouchard wrote:
> >
> > Hi, I have built an adaptor between a DB9 serial port and a DIN4 serial
> > port, and I can send characters both ways at 300 baud and at 2400 baud
> now,
> > but when I try 4800, 9600 or 19200, I get either garbage or nothing.
> >
> > This is between Terminate 5.0 in MSDOS 6.22 with UART 16550, and a CoCo 3
> > running UltimaTerm 4.1.
> >
> > Any idea on how to fix this ?
>
> I would have my doubts about UltimaTerm, especially after reading
> Aaron's reply. Or the PC side - have you tested higher speeds with
> something else than the CoCo, for instance loopback by shorting RX and
> TX on the RS232 plug? You could of course try loopback on the CoCo
> side as well.
>
> Otherwise it could be hardware problem. Some CoCos (1/2 dunno about 3)
> have an operation amplifier (741) doing signal inversion on the TX
> line, and its poor bandwidth limits the baud rate. You could try
> exchanging it. Bad connections/soldering/isolation could also cause
> increasing problems at higher speeds but it would be strange that the
> result is so binary as you experience.
>
> Tormod
>
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>



-- 
Long live the CoCo