How to use pin RA4 as digital I/O port? plz help

[goug]

I am using PIC 16F877A for a big project, I already used all available ports, but having some problems with PORTA.

I want to use PORTA as a digital I/O port. I just found in 16F877A datasheet how to configure pins 0,1,2,3 and 5 as digital I/O (ADCON1 = %00000111); but can't find how to configure pin 4.

I just can't set or clear pin 4 of PORTA

could anyone help please?

 

[Nigel Goodwin]

RA4 is an open-collector output, you need an external pull-up resistor for it to go high!.

 

[goug]

>> Using RA4 as an output (TRISA = 0) <<

I tried with the pull-up resistor on pin RA4 (1k + 5V):

Result: RA4 remains high whether it's set or cleared by the PIC!
I don't want that

What could be the problem? (maybe RA4 can not be configured as output? set and cleared when needed)

 

[picasm]

RA4 should work fine as an open collector output with a pull-up resistor to +5v.

One thing that could cause you a problem is that RA4 is also used as an output for the comparator module.
The comparator module is turned off by default at power-on, so should not cause any problem unless you have enabled it.
See section 12 of the data sheet.

 

[goug]

Thanks a lot everybody

It actually works with the pull-up resistor