From: Scott Dattalo, notes
Comments added by Alex Forencich
;******************************** ;binary_to_bcd - 8-bits ; ;Input ; bin - 8-bit binary number ; A1*16+A0 ;Outputs ; hundreds - the hundreds digit of the BCD conversion ; tens_and_ones - the tens and ones digits of the BCD conversion binary_to_bcd: CLRF hundreds SWAPF bin, W ; swap the nibbles ADDWF bin, W ; so we can add the upper to the lower ANDLW B'00001111' ; lose the upper nibble (W is in BCD from now on) SKPNDC ; if we carried a one (upper + lower > 16) ADDLW 0x16 ; add 16 (the place value) (1s + 16 * 10s) SKPNDC ; did that cause a carry from the 1's place? ADDLW 0x06 ; if so, add the missing 6 (carry is only worth 10) ADDLW 0x06 ; fix max digit value by adding 6 SKPDC ; if was greater than 9, DC will be set ADDLW -0x06 ; if if it wasn't, get rid of that extra 6 BTFSC bin,4 ; 16's place ADDLW 0x16 - 1 + 0x6 ; add 16 - 1 and check for digit carry SKPDC ADDLW -0x06 ; if nothing carried, get rid of that 6 BTFSC bin, 5 ; 32nd's place ADDLW 0x30 ; add 32 - 2 BTFSC bin, 6 ; 64th's place ADDLW 0x60 ; add 64 - 4 BTFSC bin, 7 ; 128th's place ADDLW 0x20 ; add 128 - 8 % 100 ADDLW 0x60 ; has the 10's place overflowed? RLF hundreds, F ; pop carry in hundreds' LSB BTFSS hundreds, 0 ; if it hasn't ADDLW -0x60 ; get rid of that extra 60 MOVWF tens_and_ones ; save result BTFSC bin,7 ; remeber adding 28 - 8 for 128? INCF hundreds, F ; add the missing 100 if bit 7 is set RETURN ; all done!
Note: SKPDC is equivalent to BTFSS STATUS, DC and SKPNDC is equivalent to BTFSC STATUS, DC
Same code optimized for the PIC18F instruction set:
binary_to_bcd: clrf hundreds swapf bin, W, A ; swap the nibbles addwf bin, W, A ; so we can add the upper to the lower andlw B'00001111' ; and lose the upper nibble (W is in BCD from now on) btfsc STATUS, DC, A ; if we carried a one (upper + lower > 16) addlw 0x16 ; add 16 (the place value) (1s + 16 * 10s) daw ; check for digit overflows btfsc bin, 4, A ; 16's place addlw 0x16 - 1 ; add 16 - 1 btfsc bin, 5, A ; 32nd's place addlw 0x30 ; add 32 - 2 btfsc bin, 6, A ; 64th's place addlw 0x60 ; add 64 - 4 btfsc bin, 7, A ; 128th's place addlw 0x20 ; add 128 - 8 % 100 daw ; check for digit overflows rlcf hundreds, F ; pop carry in hundreds' LSB movwf tens_and_ones btfsc bin,7, A ; remember adding 28 - 8 for 128? incf hundreds, F ; add the missing 100 if bit 7 is set return
Don't need the hundreds? Get rid of everything after the second daw up to the return. The result will end up in W in that case, just add a movwf if the result is needed elsewhere. Want to pass in the byte in W? Just add a movwf bin at the beginning.
I am a Newbie and this is the exact information i was looking for, it works great. The only thing is i don't know how this code actually works, maybe i try to figure it out when i learn more about asm.+
|file: /Techref/microchip/math/radix/b2bhp-8b3d.htm, 5KB, , updated: 2015/9/11 08:04, local time: 2019/2/15 18:51,
|©2019 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/radix/b2bhp-8b3d.htm"> PIC Microcontoller Radix Math Method Binary to BCD half-packed 8 bit to 3 digit</A>
|Did you find what you needed?|
PICList 2019 contributors:
o List host: MIT, Site host massmind.org, Top posters @20190215 David Van Horn, RussellMc, Neil, AB Pearce - UKRI STFC, James Cameron, Allen Mulvey, David C Brown, Denny Esterline, mike brown, Bob Blick,
* 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!