>-----Original Message-----
>From: Mark Beetge [ MTN - Harrington Street ]
>
>Hi Mike
>Thanks for the reply
>The board I made has the pic interfaced to a FTDI USB chip and
>I have routines to send to and receive from the board and a
>VB6 program on my pc to send commands and receive info and do
>the GUI. Both chips have a 0.1uF and 10uF tant decoupling. The
>whole board uses smd components with the caps within mm of the
>chips. The simple routine I use for doing the conversion is as follows:
>
>do_b
>                        bsf     ADCON0,GO,0             ; Start  A/D
>conversion
>adconvtst               btfsc   ADCON0,DONE,0   ;Is conversion complete
>                        goto    adconvtst               ;No, go test
>again
>
>                        movf    ADRESH,w,0              ;get high byte
>                        call    sendbyte                ;send
>it to USB
>                        movf    ADRESL,w,0              ;get low byte
>                        call    sendbyte                ;send it to USB
>
>                        goto    again                   ;back to read
>USB for command loop
>

That part looks fine.  I'm guessing you have a suitable acquisition delay
(around 15us) between setting the channel in ADCON0 and setting the GO bit?

One thing to check is that both sets of Vdd/Vss pins are definitely
connected to their respective supplies, this is just the sort of odd
behaviour that can occur if only one set of pins is powered.

Regards

Mike




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