Wow. I am certainly glad that I subscribed to this list. Thank you for all
the responses.
I will try to cover some of the points made so far:

- I will post the code I am using shortly...
- I could use a chip with a USART, but I like the idea of being in full
control of the serial comms, and had selected the 12F675 because it did
everything I needed at the lowest price
- My main aim is to achieve the sending from the chip to the PC. I have not
included anything for an RX pin on the chip at the moment
- I have read various websites (Roman Black's is one that comes to mind),
which seem to show that a direct connection between PIC and PC is possible,
including some using the 12F675
- I am seeing problems with the chip when I connect only the ground from
the PC's serial port. As soon as I pull this ground wire out the chip
starts operating again.
- I am seeing the same problems when I try to use the MAX232CPE board I
have (I would prefer to get this working without the board, because it is
being used for something else, but if necessary I can wire up a MAX232CPE
chip with the capacitors, etc...)
- In connection with the two previous points, I think Djula may be on to
something with the MCLR. I have read information from various sources, with
some suggesting pins should be grounded if not used, and others saying it
is best to leave them unconnected. At the moment, I am leaving them
unconnected if not in use. Could 'floating' pins be the problem?

Is there anything I can add to protect the chip from unwanted negative
voltage? Measuring voltage between the two ground lines with a multimeter
does seem to indicate the PC's ground line is lower by about 0.04V compared
with the batteries.

Code to follow...
--=20
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