9S12XDP512 Port M oddity when used as GPIO

[zdriver]

Hello,

I am using Port M as GPIO, the entire port is set to output.

I am currently testing the output with a bank of 8 LED's, and have found that when outputting a "1" to Bit 1 of the port, Bit 0 goes high at the same time when it should be low.  The same problem happens when Bit 3 has a "1" output to it, Bit 2 goes high at the same time!

Bit 4-7 work as expected okay, follow all outputs correctly.

 It is not a solder short on the board as I can turn on either Bit 0 or Bit 2 without affecting the higher bit.

MSCAN normally uses this Port, but micro is in the out of reset state which I believe is disabled. I'm hoping that  I have not set up the Port correctly as opposed to some bad silicon here. Any suggestions?

My setup;

                   LDAA  #255

                   STAA  DDRM       ;Set PortM DDR to output

                   LDAA  #8              ; Turn on PM 3 output

                   STAA   PTM

                                         PM3 and PM2 are now BOTH high!

                 CLRA

                 STAA   PTM          ;Turn all outputs off

                                        All outputs off normal

                LDAA  #4

                STAA  PTM           ;Turn on PM2

                                       PM2 on only as expected

[DannyM83]

The fact that the problem happens on PM0 and PM2 which are both also used for CANRX seems to point to a CAN transceiver driving the pin high.

Does the board you are using come with CAN transceivers? If so you should disable them.

Hope that helps

Danny

[zdriver]

That was it, evaluation board does have 2 transceivers in place. After some careful cutting of board  traces to RXCAN0 and RXCAN1 , I can now use the port for GPIO. Thanks for the reply.