Electronic – Configuring PIC16F877A PORTA as digital output port

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I am trying to use PORTA of PIC16F877A as digital output port. But somehow it does not seems to be working.

I am using MPLAB X IDE MPASM to assemble the code. Below is the code I am using to initialize PORTA – 

banksel PORTA;
clrf PORTA;

banksel ADCON1
movlw 0x06
movwf ADCON1

banksel CMCON
movlw 0x07
movwf CMCON

banksel TRISA
movlw 0x00
movwf TRISA

banksel PORTA
movlw 0xFF
movwf PORTA

The LEDs at the output does not glow at all. What am I missing? I am not expecting RA4 to glow as I know it requires an external pull-up resistor but what about other LEDs.

Any help would be much appreciated. Thanks in advance.

Best Answer

It looks like this code, such as it is, is setting up the digital outputs correctly. It is good that you used BANKSEL to eliminate any issue of possibly bad bank setting. However, this code still has some serious problems:

  1. There is not a single comment in sight.

  2. How did this ever assemble!? Opcodes aren't allowed in column 1.

  3. Just using a HEX constant for a number of bit fields is irresponsible programming, such as your "MOVLW 0x07". The code should be explaining what each individual bit field is and what you are therefore setting it to. Something like this:

        banksel blonkcon1
    movlw   b'10010010'
            ; 1-------  enable the blonkulator module
            ; -XX-----  unused
            ; ---10---  prescaler of 7
            ; -----010  select single-shot operation
    movwf   blonkcon1

To test the pin setup by itself, disconnect the LEDs and just look at what the pins are doing with a scope. There is a good chance your problem is with the circuit. Show the complete circuit.

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