The substract code I posted is bad, I don't know what happened. Here is
the fixed version:

On Mon, 7 Oct 2002, Peter L. Peres wrote:

*>On Sun, 6 Oct 2002, Joaquim J. Peixoto wrote:
*>
*>*>This is not a direct solution to your problem but an attempt to rethink it.
*>*>
*>*>Why add in BCD? It seems unnatural on a PIC. If you are using a PIC, then
*>*>the natural method would be binary addition.
*>
*>The natural way to store data in a micro with limited space and limited
*>maths is packed BCD. Then you need half the storage space of unpacked BCD,
*>and no base conversions.
*>
*>In C the code is like:
*>
*>uchar pbcd;     // packed bcd accumulator
*>bit   carry;    // carry in and out, normally LSB in some register, or
*>                // use the one in STATUS
*>
*>// add one packed BCD byte to another, returns carry out
*>uchar pbcd_add( uchar addend ) {
*>
*>  pbcd += addend;            // this is clear
*>  if(carry)                  // so is this
*>    ++pbcd;
*>
*>  if((pbcd & 0x0F) > 0x09)   // need daa lsbyte
*>    pbcd += 0x06;
*>
*>  carry = 0;                 // assume no carry out
*>  if((pbcd & 0xF0) > 0x90) { // need daa msbyte
*>    carry = 1;
*>    pbcd += 0x60;
*>    return(1);               // carry
*>  }
*>  return(0);
*>}
*>
*>// substract a packed BCD number from another
*>void pbcd_sub( uchar subtrahend ) {
*>
*>  pbcd -= subtrahend;
*>  if(carry)
*>    --pbcd;
*>
*>  if((pbcd & 0x0F) > 0x09)    // need to saa lsbyte
*>    pbcd -= 0x06;     // fixed
*>
*>  carry = 0;
*>  if((pbcd & 0xF0) > 0x90) { // fixed
*>    carry = 1;
*>    pbcd -= 0x60;     // fixed
*>    return(1);
*>  }
*>  return(0);
*>}

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