Parallel circuit question

[helloleong]

I got a circuit problem to ask.

Here is the circuit diagram
**broken link removed**

The question i wanna ask is when the PIC send a 0v and at the same time EM module send 5V, what signal will the controller detect?

This circuit is done by the previous trainee engineering.
The PIC is the reader to detect button press and read card.
So the EM module is use to read card. When no card was read D0 and D1 always stay high (5V). When card present it will send out 0 pulse.

So i had set the pic 2 pin to input to detect read card
And set to output when button press, if the button press signal finish send to the controller it will set back to input to detect card.

It still works, but some times the controller cannot detect signal send.
And my boss said reader hang, and ask me why.
But just the controller no response, the reader still running as usual.

Thank you

 

[ericgibbs]

hi,
The output driver pins on the PIC should not be connected to output driver pins on the EM, the voltage levels on the lines will be indeterminate and will give the problems you are experiencing.

 

[helloleong]

Hi, Ericgibbs. Thanks for your reply. I had told my boss, and there are changing the PCD design.