From: Mike Keitz. There is a trick method that works for 4 bits. It replaces a 2-bit number in a variable with a 4-bit mask:
incf BitP, W ;W = 0001 0010 0011 0100 btfsc BitP, 1 ;If 0 or 1, result is almost correct now. iorwf BitP, F ;BitP = [0000] [0001] 0011 0111 incf BitP, F ;BitP = 0001 0010 0100 1000
It could be the core of an 8-bit routine thus:
; Convert 3-bit number (0-7) in INDEX to a 8-bit mask (00000001 ... ; 10000000) in BitP. movfw INDEX andlw b'00000011' ;Start with half of the mask. movwf BitP incf BitP, W ;The 4-bit converter btfsc BitP, 1 iorwf BitP, F incf BitP, F btfsc INDEX, 2 ;Is it high 4 bits? swapf BitP, F
Code:
+Still, a simple table lookup or 8-bits is less instruction cycles and doesn't need a temp register. And it can do a little math too (set bit 7-WREG instead of bit WREG) GET_BIT ADDWF PCL,F RETLW B'00000001' RETLW B'00000010' RETLW B'00000100' RETLW B'00001000' RETLW B'00010000' RETLW B'00100000' RETLW B'01000000' RETLW B'10000000' GET_BIT2 ADDWF PCL,F RETLW B'10000000' RETLW B'01000000' RETLW B'00100000' RETLW B'00010000' RETLW B'00001000' RETLW B'00000100' RETLW B'00000010' RETLW B'00000001'
file: /Techref/microchip/math/bit/mask.htm, 2KB, , updated: 2008/10/8 05:23, local time: 2023/6/5 00:17, |
©2023 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://massmind.org/techref/microchip/math/bit/mask.htm"> PIC Microcontoller Bit Math Method Converting a 3-bit number to a 8-bit mask</A> |
Did you find what you needed? |
Welcome to massmind.org! |
Welcome to massmind.org! |
.