Andreas Magnusson wrote:
>
> Hello!
>
> I have a problem.... I have programmed a "test program" for a robot I have
> built (PIC16F84 used). The program controlls a stepmotorcard. Everything
> seems to work exept one thing RB3 pin is allways high... The pin should
> pulse like the other ones. I have checed the circuitboard and also tested
> with two different MCU:s. I programmed a small program to only clear portb
> it worked. I cant really understund why the pin allways is high....

Hi,

It is caused by the infamous read-modify-write problem.  See code
modifications below:


> M3A
>          CLRF PORTA
>          BSF PORTB,6
>          BCF PORTB,7
Change the last 2 lines by:
        movlw   B'01000000'
        movwf   PORTB

> M3TABLE
>          MOVF M3,W
>          CALL FTABLE
>          MOVWF PORTB
>          NOP
>          BCF PORTB,6                        ;clocking in the value from
>          NOP
>          BSF PORTB,6
change the last 4 lines by:
        andlw   B'10111111'
        movwf   PORTB
        iorlw   B'01000000'
        movwf   PORTB

regards,
Reggie

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