On 05-Jan-12 14:10, Adam Walley wrote:
> 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 mu=
ch
> 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 wirin=
g
> right first.
>
> The laptop's serial pins appear to be operating at -9.6/+9.6V. I can crea=
te
> 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.

Check if MCLR pin is floating and restarting the PIC randomly.

Write a program that blinks the LED only once, connect the battery and=20
try to touch the MCLR pin with your hand or a metallic object. If it=20
doesn't reset, connect the ground wire.

The decoupling capacitor should be very close to PIC, not on the battery=20
or somewhere in the middle.

Djula
--=20
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