Thanks for the reminder, I made that mistake once or twice myself.

On the assumption that 0x70 and 0x80 are valid packed bcd numbers
I just finished a simple test to isolate the problem. The shortened version
of
the code goes like this;

(Note: 18F452 processor, checking apparent addwfc and/or daw problem)

         cblock 0x00
         binvar:1
         bcdval:1
         end

     clrc
     movf         binvar,w
     addwfc     binvar,w
     daw
     movwf      bcdval

Test 1:
    set binvar = 0x70
    after the addwfc, WREG = 0xE0     Carry = 0
    after the daw,      WREG = 0x40     Carry = 1
     So far so good!

Test 2
    set binvar = 0x80
    after the addwfc, WREG = 0x00     Carry = 1
    after the daw,      WREG = 0x60     Carry = 0
    What happened to the carry bit ?? I rather expected it to still be
there.

In fairness, the data sheet doesn't say much about how or why the
carry bit is affected, it just say that it is affected. There may be other
documents that give more detailed information about the status bits
during and after a 'daw' but I haven't found any yet.

Going back to the original problem: I don't know how completely valid
this is yet but, after a very brief test,  it appears that if  I save the
carry
bit after the addwfc and restore it after the daw, all may be well.

Mike Jones

----- Original Message -----
From: "Jan-erik Svderholm (QAC)" <Jan-erik.Soderholm@PAC.ERICSSON.SE>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, February 04, 2003 12:11 AM
Subject: Re: [PIC]: Binary to Packed BCD Conversion Problem


I wrote a routine to convert a bin value to BCD
some time ago. One thing that I missed about the
DAW instruction, is that DAW "Decimal adjust W" when
W containes the result of an addition of two other
values *which both was in BCD format before the addition*.

So you can not add two *binary* values and then use
DAW on the result. You'll get all kinds of funny
results.

(And if one read the data sheet carefully, this is
clearly written there...)

I have not checked is this is the case for your code,
but anyway...

Jan-Erik Svderholm.

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