Checking push buttons on PIC16F877

Question

I began to study PIC assembly and I have one issue with PIC16F877 related with push buttons. Firstly, I show you configuration:

I want to check if SW04,SW05,SW06,SW06,SW11 are pressed, but I guess RB7 is responsible for SW07 and SW11. Will it cause problems, if I will only check for RB7, because in one function I must check SW07 and SW11 buttons.

Answer 1

No, it is not going to cause problems because when you check RB7 at certain moment of time you know for sure what line caused the signal: RB2 or RB1. If you register RB7 and RB1 is the active one, that means SW07 is pressed, if RB2 is active - then SW11 is pressed. I am assuming your program moves the logic '1' from RB0 to RB3 and every line has '1' at certain moment whilst others are Zeros.

Answer 2

No worries. Turning on pull-up resistors at RB4-RB7 inputs should not cause problems, it is just the determined state of input when it is in tri-state. These inputs should work well and normally see what RB0-RB3 outputs give them: '0' or '1'. By the way you can choose between two methods: when '0' moves among RB0-RB3 and others are '1', or when '1' moves around the RB0-RB3 among zeros. Depending on this you are scanning for '0' or for '1' respectively at RB4-RB7.