On Fri, 18 Jun 2004, Bob Japundza wrote:

> Hi All,
>
> I was wondering if my code below can be made to be a bit better.  It works fine as is, but just seems to be a bit clunky to me.  In a nutshell what I'm doing here is checking two buttons on port A, turning off/on the motor and if one button is pressed, that dictates motor direction.  I'm wondering if there's a way without using the temporary register "button_status" to check the the two bits I'm looking at.
>
> movlw b'00001100'
> andwf PORTA,W                           ;mask all but the RA2,3 bits
> movwf button_status
> movlw b'00001100'
> xorwf button_status,w
> btfsc STATUS,Z                          ;are both buttons pressed?
> goto stopmotor                          ;yes, stop the motor
> movlw b'00001100'
> andwf button_status,w
> btfsc STATUS,Z                          ;are both buttons not pressed?
> goto stopmotor                          ;yes, stop the motor
> btfsc PORTA,2                           ;check if up button is on
> goto motorup
> btfsc PORTA,3                           ;check if down button is on
> goto motordown

Well, since you're willing to perform btf operations on an I/O port, then
you could do this:

      btfsc    PORTA, RA3
       goto    RA3_is_high

      btfsc    PORTA, RA2
       goto    motorup            ; RA3:RA2 = 01
      goto     stopmotor          ; RA3:RA2 = 00

RA3_is_high:

      btfss    PORTA, RA2
       goto    motordown            ; RA3:RA2 = 10

    ; RA3:RA2 = 11

stopmotor:

Scott

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