I am using a 12C509 to read four switches.  I have /MCLR enabled so that GP3 is
not
an input.  I also have GP0 as an output and I am running off of the internal R/C
oscillator (freeing up GP4,5).

Thus I have GP1,2,4,5 as inputs reading the switches.  I want to take the four
inputs and place them in the high nybble of W so that:
        GP1 = Bit4 = Switch A
        GP2 = Bit5 = Switch B
        GP4 = Bit6 = Switch C
        GP5 = Bit7 = Switch D

Here's what I wrote:

        ; READ THE SWITCHES
        MOVF    GPIO,W  ; W = 00DC0BA0
;
        ; SHIFT BITS TO ALIGN WITH THE HIGH NYBBLE
        BTFSC   W,5     ; is GP5 (pin 2) HI?
        BSF     W,7     ; if it is, then Bit7=HI
        BTFSC   W,4     ; is GP4 (pin 3) HI?
        BSF     W,6     ; if it is, then Bit6=HI
        ANDLW   0x0C6   ; W = DC000BA0
        BTFSC   W,2     ; is GP2 (pin 5) HI?
        BSF     W,5     ; if it is, then Bit5=HI
        BTFSC   W,1     ; is GP1 (pin 6) HI?
        BSF     W,4     ; if it is, then Bit4=HI
                        ; W = DCBA0BA0
;
        ; MASK OFF LOW NYBBLE
        ANDLW   0x0F0   ; W = DCBA0000

It looks right to me but I am getting flakey results and I am suspicious of the
bit
manipulation.  It is late Sunday night in California and of course I have a demo
 in
twelve hours...

Can anyone see a flaw here?  Is there a better way of shifting the bits?

My read of the datasheet says that bits 0,3,6,7 of GPIO (all non-inputs) should
read as 0's right?  I mean I don't need an ANDLW 0x036 after the read of GPIO or
something?

Any help appreciated,

Michael

* TAKE THE '.NOSPAM' OUT OF MY ADDRESS TO REPLY
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