8-bit Microcontrollers中的主题 Re: DIV in HCS08

DIV in HCS08

Zohreh — Mon, 03 Nov 2008 08:28:37 GMT

Hello All,

I'm new to the field and to the forum.

I'd like to divide a 16bit by 10 repeatedly (to display it in decimal).

As MC9S08AW60 supports 16 by 8 bit Division, and the quotient and Remainder are each one byte, I do not know how to manage that? I expect 2 bytes for Q!

Will you explain in an easy language as English is not my first language?

Thanks in advance

Zohreh

Re: DIV in HCS08

bigmac — Mon, 03 Nov 2008 11:44:37 GMT

Hello Zohreh, and welcome to the forum.

I assume that you are using assembly code.

Since the result of a division (by 10 decimal) may be 16-bits length, the process becomes "long division" using the DIV instruction twice, once for each byte of the 16-bit value. After the first division (starting with H = 0), the remainder within H becomes the most significant byte for the second division.

This is demonstrated in the following assembly code sub-routine. Each decimal digit value is stored on the stack until four digits have been processed, and ACC contains the MS digit. Each digit is then converted to ASCII, and stored in BUF.

;**************************************************************
; 16-BIT BINARY TO 5-DIGIT BCD CONVERSION
;**************************************************************
; On entry, first two bytes of BUF contain binary number.
; On exit, the six bytes of BUF contain null terminated numeric
; ASCII data string.

CONVERT: LDX    #4             ; Number of divisions required
          STX    BUF+5
          LDX    #10            ; Divisor
CNV1:     BSR    DIVIDE
          PSHH                  ; Store remainder to stack
          DBNZ   BUF+5,CNV1     ; Loop for next digit

          ADD    #'0'           ; Convert to numeric ASCII
          STA    BUF            ; MS digit
          CLRX                  ; Buffer index
CNV2:     PULA                  ; Get value from stack
          ADD    #'0'           ; Convert to numeric ASCII
          STA    BUF+1,X
          INCX
          CPX    #4             ; Test for maximum digits
          BLO    CNV2           ; Loop if not
          RTS

DIVIDE: CLRH

          LDA    BUF
          DIV
          STA    BUF
          LDA    BUF+1
          DIV
          STA    BUF+1
          RTS

Regards,

Mac

Message Edited by bigmac on 2008-11-03 02:53 PM

Re: DIV in HCS08

Zohreh — Mon, 03 Nov 2008 16:32:50 GMT

Thank you so much Mac.

You helped me a lot.

Zohreh

Re: DIV in HCS08

bigmac — Mon, 03 Nov 2008 17:38:33 GMT

Hello Zohreh,

I have just noticed that there is an error within my previous code. Prior to the CNV2 label, an additional CLRH instruction will be necessary. Otherwise the subsequent instruction STA BUF+1,X will point to the incorrect memory location.

Regards,

Mac

Re: DIV in HCS08

tonyp — Mon, 03 Nov 2008 20:39:35 GMT

And here's another version which is fully stack-based (re-entrant), suppresses leading zeros, and prints the result. (Just point PutChar to the address of the routine which prints a single ASCII character in RegA.)

                    #ROM

;*******************************************************************************
; Purpose: Print a number as decimal ASCII string
; Input : XA = 16-bit number to display as ASCII string (if entering from PrintWordXA)
;        : HX = 16-bit number to display as ASCII string (if entering from PrintWordHX)
; Output : None

PrintWordXA         txh                           ;H = dividend (MSB)
                    tax                           ;X = dividend (LSB)

PrintWordHX         clra
                    psha                          ;ASCIZ terminator

?PrintWord.Loop     pshhx                         ;save (current) dividend

                    ldhx      #10                 ;H = 0 (always), X = divisor (10)
                    pula
                    div
                    psha
                    lda       2,sp
                    div
                    sta       2,sp

                    tha                           ;A = remainder
                    add       #'0'                ;convert to ASCII
                    pulhx                         ;remove dividend from stack
                    psha                          ;save next result byte (right to left)
                    cphx      #0                  ;while dividend not zero...
                    bne       ?PrintWord.Loop     ;... keep going

?PrintWord.Print    pula                          ;get next ASCIZ char
                    cbeqa     #0,?PrintWord.Done ;on terminator, exit
                    jsr       PutChar             ;else, print digit
                    bra       ?PrintWord.Print

?PrintWord.Done     rts

Message Edited by tonyp on 2008-11-03 03:06 PM

Re: DIV in HCS08

bigmac — Tue, 04 Nov 2008 00:41:14 GMT

Hello,

It is probably worth mentioning that TonyP's code uses a number of macros that have not been defined within the code snippet. Substitute the following instruction sequences in place of each macro.

TXH macro is equivalent to:

pshx

pulh

THA macro is equivalent to:

pshh

pula

PSHHX macro is equivalent to:

pshh

pshx

PULHX macro is equivalent to:

pulx

pulh

Regards,

Mac

Re: DIV in HCS08

tonyp — Tue, 04 Nov 2008 00:46:09 GMT

Thanks bigmac, I always forget to mention that.

It is also worth mentioning that since the leading zeros are suppressed, you can easily expand the routine for bytes, too. Just add one more entry point and a few PUSH/PULL instructions to protect the registers from destruction. Attached is the final version.

Message Edited by tonyp on 2008-11-03 06:48 PM

Re: DIV in HCS08

tonyp — Tue, 04 Nov 2008 01:18:51 GMT

Oops! The order is actually reverse, to be consistent with big-endian.

PSHHX
pshx
pshh

PULHX
pulh
pulx

bigmac wrote:
PSHHX macro is equivalent to:
   pshh
   pshx

PULHX macro is equivalent to:
   pulx
   pulh

Message Edited by tonyp on 2008-11-03 07:20 PM