; Content of "U_b" before, during & after the conversion:
; (L/H stand for LOW/HIGH - Nibble)
;
;  positive argument:
;  adr  in          out
;------------------------------
;  +5         L0    D(100,000)
;  +4         H0    D(10,000)
;  +3   A3    L1    D(1,000)
;  +2   A2    H1    D(100)
;  +1   A1    L2    D(10)
; &U_b  A0          D(1)

;  negative argument:
;  adr  in          out
;------------------------------
;  +5               '-'
;  +4         L0    D(10,000)
;  +3   A3    H0    D(1,000)
;  +2   A2    L1    D(100)
;  +1   A1    H1    D(10)
; &U_b  A0    L2    D(1)

;  Content of the registers during conversion:
;  (main loop, "LOOP_DIGIT")
;
;  R0 ... "Nibble" Pointer
;  R1 ... "Digit" Pointer
;  R2 ... "Nibble" Counter
;  R3 ... "Digit" Counter

;  positive argument:
;  R0    R1    R2    R3
;  +1    0     5     6
;  +1    +1    5     5
;  +2    +2    4     4
;  +3    +3    3     3
;  +4    +4    2     2
;  +5    +5    1     1

;  negative argument:
;  R0    R1    R2    R3
;  0     0     5     5
;  +1    +1    4     4
;  +2    +2    3     3
;  +3    +3    2     2
;  +4    +4    1     1

;--------------------------------------

$XREF
$NOMOD51

B  DATA  0F0H
ACC   DATA  0E0H
NAME  BCD

?PR?bin2bcd?BCD      SEGMENT CODE
EXTRN DATA (U_b)
PUBLIC   bin2bcd

   RSEG  ?PR?bin2bcd?BCD
   USING 0

bin2bcd:

   MOV   A,U_b
   JNB   ACC.7,POSITIVE
   
   CLR   C                    ; negative argument 
   CLR   A
   SUBB  A,U_b+3
   MOV   U_b+3,A
   CLR   A
   SUBB  A,U_b+2
   MOV   U_b+2,A
   CLR   A
   SUBB  A,U_b+1
   MOV   U_b+1,A
   CLR   A
   SUBB  A,U_b
   JNZ   ERROR             ; should be ZERO
   
   MOV   R3,#5             ;"Digit" Counter
   MOV   R1,#U_b           ;"Digit" Pointer
   MOV   R2,#5             ;"Nibble" Counter
   MOV   R0,#U_b           ;"Nibble" Pointer


   MOV   U_b+5,#0FH        ; 0x0F as '-' Character 
                           ; (will be converted for 
                           ;  7-seg. LCD)

   MOV   A,U_b+1           ; LSB2 LN -> 0
   MOV   U_b,A
   ANL   U_b,#0FH   

   ANL   A, #0F0H          ; should be ZERO
   JNZ   ERROR

   MOV   A,U_b+3           ; LSB0 LN -> 4
   MOV   U_b+4,A
   ANL   U_b+4,#0FH
   SWAP  A
   MOV   U_b+3,A           ; LSB0 HN -> 3
   ANL   U_b+3,#0FH

   MOV   A,U_b+2           ; LSB1 LN -> 2
   ANL   U_b+2,#0FH
   SWAP  A
   MOV   U_b+1,A           ; LSB1 HN -> 1
   ANL   U_b+1,#0FH

   CLR   A
   SJMP  LOOP_DIV    ; everything is in place now
   
POSITIVE:

   MOV   A,U_b+1
   ANL   A, #0F0H          ; should be ZERO
   JNZ   ERROR

   MOV   A,U_b+3           ; LSB0 LN -> 5
   MOV   U_b+5,A
   ANL   U_b+5,#0FH
   SWAP  A
   MOV   U_b+4,A           ; LSB0 HN -> 4
   ANL   U_b+4,#0FH

   MOV   A,U_b+2           ; LSB1 LN -> 3
   MOV   U_b+3,A
   ANL   U_b+3,#0FH
   SWAP  A
   MOV   U_b+2,A           ; LSB1 HN -> 2
   ANL   U_b+2,#0FH

   ANL   U_b+1,#0FH        ; LSB2 LN -> 1

   MOV   R3,#6             ;"Digit" Counter
   MOV   R1,#U_b           ;"Digit" Pointer
   MOV   R2,#5             ;"Nibble" Counter
   MOV   R0,#U_b+1         ;"Nibble" Pointer

   CLR   A
   SJMP  LOOP_DIV    ; everything is in place now

LOOP_DIGIT:     

   MOV   AR0,AR1
   MOV   AR2,AR3
   CLR   A

LOOP_DIV:
   XCHD  A,@R0
   MOV   B,#10       ; DIVISOR
   DIV   AB
   XCHD  A,@R0
   MOV   A,B
   SWAP  A           ; Remainder in AKKU HIGH NIBBLE
   INC   R0
   DJNZ  R2,LOOP_DIV

   MOV   A,@R1        ; should be ZERO
   JNZ   ERROR
   MOV   @R1,B
   INC   R1
   DJNZ  R3,LOOP_DIGIT

END1:
   RET

ERROR:
   MOV A,#0FH         ; 0x0F as '-' Character 
   MOV U_b,A
   MOV U_b+1,A
   MOV U_b+2,A
   MOV U_b+3,A
   MOV U_b+4,A
   MOV U_b+5,A

END2:   
   RET

   END