[time-nuts] Rapco 1804M - serial problems?

David J Taylor david-taylor at blueyonder.co.uk
Tue Oct 18 02:49:41 EDT 2011

> 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!)

SatSignal software - quality software written to your requirements
Web:  http://www.satsignal.eu
Email:  david-taylor at blueyonder.co.uk 

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