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

Hal Murray hmurray at megapathdsl.net
Tue Oct 18 03:36:11 EDT 2011


> So,  remarkable as it is, it seems that either the serial chip is bad, or
> bad  data is being sent to the chip.

You might collect a pile of errors and analyze the bit level changes.

I think some of your errors were / changing to a ?.  That's hex 2F changing 
to 3F, or picking the 10 bit.  How many of the other errors did the same 
thing?

I think serial ports are least significant bit first, so a scope would see 
11110100 changing to 11111100.  That would be a reasonable error on a serial 
port if the high-low-high transition was slow and didn't get low enough.  
(But 4800 is really slow and you said the cable was short.  Any problems 
should be obvious on a scope.)

Do you have any other serial ports where you could try it?  How about a 
serial-USB dongle?  Or maybe even a shorter cable?



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