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"!

-- 
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist