; Div8 divides a 16-bit-number by a 8-bit-number ; Test: 16-bit-number: 0xAAAA, 8-bit-number: 0x55 ; .NOLIST .INCLUDE "8515def.inc" .LIST ; ; Registers ; .DEF rd1l = R0 ; LSB 16-bit-number to be divided .DEF rd1h = R1 ; MSB 16-bit-number to be divided .DEF rd1u = R2 ; interim register .DEF rd2 = R3 ; 8-bit-number to divide with .DEF rel = R4 ; LSB result .DEF reh = R5 ; MSB result .DEF rmp = R16; multipurpose register for loading ; .CSEG .ORG 0 ; rjmp start ; start: ; ; Load the test numbers to the appropriate registers ; ldi rmp,0xAA ; 0xAAAA to be divided mov rd1h,rmp mov rd1l,rmp ldi rmp,0x55 ; 0x55 to be divided with mov rd2,rmp ; ; Divide rd1h:rd1l by rd2 ; div8: clr rd1u ; clear interim register clr reh ; clear result (the result registers clr rel ; are also used to count to 16 for the inc rel ; division steps, is set to 1 at start) ; ; Here the division loop starts ; div8a: clc ; clear carry-bit rol rd1l ; rotate the next-upper bit of the number rol rd1h ; to the interim register (multiply by 2) rol rd1u brcs div8b ; a one has rolled left, so subtract cp rd1u,rd2 ; Division result 1 or 0? brcs div8c ; jump over subtraction, if smaller div8b: sub rd1u,rd2; subtract number to divide with sec ; set carry-bit, result is a 1 rjmp div8d ; jump to shift of the result bit div8c: clc ; clear carry-bit, resulting bit is a 0 div8d: rol rel ; rotate carry-bit into result registers rol reh brcc div8a ; as long as zero rotate out of the result ; registers: go on with the division loop ; End of the division reached stop: rjmp stop ; endless loop