Brent, you seem to have hit on the answer!  I reverted to an old version 
of my code and mixed the setup around a bit, and suddenly it started 
working!

I think the trick was putting the ANSEL and ANSELH initialization 
earlier in the process, but I'm not positive since I moved a lot of 
things at once. 

I'm new to this site, so if there is any place I should post my working 
code and/or do something else to contribute to the global PIC knowledge 
base, please let me know.

Thank you all for your suggestions,
Tom


Brent Brown wrote:
> On 15 Apr 2009 at 15:43, Tom Cassidy wrote:
>
>   
>> I'm sending the PIC signals through a MAX3232E chip.  I've used the same 
>> circuit many times, and even with other PIC chips.  And it's working 
>> fine when the PIC sends a character to the PC.
>>
>> When I hook a scope up to the RX pin of the PIC16F690 (Pin 12) I see a 
>> +5v marking signal as the default, and it spaces to 0 volts as I send a 
>> character from the PC.
>>
>> I should have mentioned that I hooked up the PICkit2 16F887 demo board 
>> to this same RS232-TTL converter, by removing the '690 from my board and 
>> jumpering wires from the '887 to the pads.  I used much the same code as 
>> for the '690.  This circuit worked, sending and receiving characters as 
>> expected.
>>
>> This has really got me stumped!
>>     
>
> Sounds like software like you say. I'd be checking the precise order of initialisation, 
> and TRIS status for the port lines according to the data sheet. I recently swapped 
> the order of initialisation routines in a working '886 project thinking it wouldn't hurt 
> anything - passed my own tests but a while later showed up problems in the field. 
> Turned out if characters were being received WHILE the USART was being 
> initialised it would send but not receive (or the other way round, can't remember 
> exactly) and baud rate was sometimes messed up. It was hard to reproduce the 
> symptoms, and debugging led me to my own comments in the code... "this 
> shouldn't affect anything"!
>
>   
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