Do you have a scope?
I'd check the voltage levels, the bit timing, and the rise/fall times.
You
can also check the timing on the receiving system by getting it to send
something.
Sometimes the UART uses a handy clock that doesn't generate exact
frequencies. Usually that's only a problem at faster baud rates.
If the driver is weak, the rise time might be a problem. (But 4800 is
very
slow.)
If that all looks good, I'd expect there is some sort of noise. How
long is
the run? How close are the grounds? Try disconnecting the DB-9 at the
receiver and putting the scope on the ground pin.
Many thanks for your suggestions, Hal. I've been through most of them,
levels are good +/- 7 V), timing is good, rate is within a couple of Hz of
4800, noise is non-existent, it's all close together (2-3 m). The same
RS-232 port talks correctly to a Garmin 12 XL and an Icom R8500. So,
remarkable as it is, it seems that either the serial chip is bad, or bad
data is being sent to the chip.
(With all the things to set - baud rate, male/female, 9/25-pin,
terminal/computer, hard/soft/no handshake, parity. stop bits - it reminds
of how easy USB or network connections have now become! At least they
usually are!)
Cheers,
David
--
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
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