[Coco] serial port problem

[Tormod Volden]

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