movf A,W   ;       w -> 13
subwf B,W   ;   w - 6 = 7
btfsc STATUS,C    ;    STATUS,C = 0 ?
goto ET1          ;     da
         ;    ne

;********************************
;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!