Setting several output-pins at a time, but not all - Electronic Circuits Projects Diagrams Free

egh01 · 25th September 2003, 06:36 PM

Lets say I use 4 pins on PORTB (we're talking 16f84a here) connected as data lines to a LCD display in 4-bit mode. If I want to send something to the LCD I would to something like this:
-movlw 'H'
-swap the nibbles
-AND with 0x0f to clear out the upper bits
-movwf PORTB

But this would make all ouput use of the other 4 pins on PORTB impossible wouldn't it? I mean this would set those pins to zero no matter if I want to or not. How are input pins affected? How would you solve this?
I guess there is a simple solution for this that I have missed. I don't want to check all the bits of the swaped byte and then manually set or clear all the pins, that feels like a pretty cycle-consuming method.

Exo · 25th September 2003, 07:09 PM

Code:

MOVLW    'H'
MOVWF    TempVar            ;save the value
SWAPF    TempVar, W         ;and swap its nibbles, save to W
ANDLW    b'00001111'        ;AND with 0x0f to clear out the upper bits 
MOVWF    TempVar            ;save it temporary
 
MOVF     PORTB, W           ;copy portb value to W
ANDLW    b'11110000'        ;'And' it so only the upper 4 bits remain
IORWF    TempVar, W         ;OR the value with W; save to W
MOVWF    PORTB              ;save to portb

egh01 · 25th September 2003, 07:22 PM

Oh so thats how you do, that was smart and simple.

Thanks!

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25th September 2003, 06:36 PM	(permalink)
egh01	Setting several output-pins at a time, but not all Lets say I use 4 pins on PORTB (we're talking 16f84a here) connected as data lines to a LCD display in 4-bit mode. If I want to send something to the LCD I would to something like this: -movlw 'H' -swap the nibbles -AND with 0x0f to clear out the upper bits -movwf PORTB But this would make all ouput use of the other 4 pins on PORTB impossible wouldn't it? I mean this would set those pins to zero no matter if I want to or not. How are input pins affected? How would you solve this? I guess there is a simple solution for this that I have missed. I don't want to check all the bits of the swaped byte and then manually set or clear all the pins, that feels like a pretty cycle-consuming method.

25th September 2003, 07:22 PM	(permalink)
egh01	Oh so thats how you do, that was smart and simple. Thanks!