;from Paul W. Webster MOVF file,W ANDLW fmask ; fmask for bit 0 is defined as 0x01 IORWF shadA,W ; add in desired outputs from shadow MOVWF PORTA
Only changes port A on the last cycle. Note that you must call this routine (subroutine/ macro) *whenever* you write to an output bit, which you always do using a BSF or BCF on shadA, never PORTA. You might also consider appending a
MOVWF shadAto keep shadA synchronized with the last byte written to PORTA.
;from Paul W. Webster ; WARNING: may trigger the "read-modify-write glitch" MOVF file,W XORWF PORTA,W ; derive "difference" value. ANDLW fmask ; fmask for bit 0 is defined as 0x01 XORWF PORTA,F ; Flip bit if not same.
We never use the following instructions on an output register like PORTA:
BSF PORTA,bit // don't do this! BCF PORTA,bit // don't do this either! IORWF PORTA,F // or this! XORWF PORTA,F // this either!because we want to avoid the "Read-Modify-Write problem" . Instead, we do the BSF or BCF on a byte of RAM (the "shadow register"), then copy that byte to the output register.
|file: /Techref/microchip/math/bit/cbrpwoj.htm, 1KB, , updated: 2005/11/8 23:39, local time: 2021/10/16 20:03,
|©2021 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/microchip/math/bit/cbrpwoj.htm"> PIC Microcontoller Bit Math Method Transfer one bit from a file register to one pin of PORT w/o jitter</A>
|Did you find what you needed?|
PICList 2021 contributors:
o List host: MIT, Site host massmind.org, Top posters @20211016 Neil, Harold Hallikainen, RussellMc, Alan Pearce, Bob Blick, Allen Mulvey, Sean Breheny, Dwayne Reid, Justin Richards, madscientistatlarge,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!