Hello,

I have been struggling to establish communication between my laptop and a
pic12f675. I am needing some help to get this working, because it's
starting to drive me nuts. I have tried various methods, but the
show-stopper always seems to be when I connect the laptop's serial ground
to the PIC's. I'm sure I am making some basic mistakes, but don't have much
electronics experience. My set-up is as follows:

- 5V power supply (4xAA rechargeable cells) with de-coupling capacitor
across + and - lines
- 12F675 microchip
- laptop with usb-serial adapter listening on COM port with Hyperterminal
- some simple PIC code, which blinks an LED on one pin, and transmits a
bit-banged letter 'K' at 9600 8N1 on a second pin

I would like to get to the stage where I can fine-tune my code, as I
suspect it will need some corrections, but I really need to get the wiring
right first.

The laptop's serial pins appear to be operating at -9.6/+9.6V. I can create
random characters by simply shorting the DTR and RX lines.

I also have a ready-made MAX232CPE board, which works very well between a
PC and a Motorola phone. I have tried to use this with the PIC, but come up
against the same problem: as soon as I connect the ground lines the PIC
stops working (blinking LED stops).

I have read as many tutorials and FAQs as I could find on the web, have
tried different approaches with transistors and mosfets, but still cannot
get this working.

One more point: I have attempted the same exercise with my Desktop PC on
its serial port, but only get the same results (which hopefully rules out
the USB adapter as the culprit).

Any help would be appreciated.
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