At 20:30 27/12/99 -0600, you wrote:
>Hello,
>
>I just started to learn Pic programming.  Can someone comment on my coments
>about this program?
>
>org     0
>
>clrf    PORTB                   ; Clear all the bits in PortB
>This line clears PORTB to all 0's right?
>
>bsf     STATUS, RP0             ; Goto bank 1 to set port direction
>This switches to bank 1
>
>bcf     TRISB & 0x07f, 0        ; Set bit 0 to output
>Here is where I have trouble.  If I understand this correctly,  this should
>take 00000000 and (and) it
>with 01111111.  Am I right?

No, it takes the address of TRISB (86h) and ANDs this with 7Fh to give the
result of 06h. This is the address of the PORTB i/o register in fact. The
setting of RP0 in the status reg provides bit-7 of the TRISB address. The
,0 specifies the I/O bit and has nothing to do with the ANDing operation.

So:

bsf     STATUS, RP0             ; Goto bank 1 to set port direction
bcf     TRISB & 0x07f, 0        ; Set bit 0 to output
bcf     STATUS, RP0             ; Go back to bank 0

Is the same to the PIC assembler as:

bsf     STATUS, RP0             ; Goto bank 1 to set port direction
bcf     PORTB, 0              ; Set bit 0 to output
bcf     STATUS, RP0             ; Go back to bank 0

But which is easier for the poor old Human to read and tells YOU exactly what
the code is doing?

BTW, We are only making bit-0 an output in the above example. The other
Data direction Bits are not changed.

Jim


>
>end
>
>Another thing I want to know is how can you clear PortB if you don't switch
>banks first?  I mean according to Mykes book,  which is where I copied this
>program from, the above code says it is ok to clear PortB, but to set the
>I/O direction, you need to switch banks first.
>
>TIA,
>Brian
>********************************************
>Better Produce through Better Control
>********************************************
>
Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: newfound@pipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________