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DAA (SPC700): Difference between revisions

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(→‎See Also: SED, CLD)
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# Then, if either the [[half-carry flag]] is set, or the lower nibble of the accumulator exceeds 0x09, add 0x06 to the accumulator.  This corrects the ones column and possibly increments the tens column by one.
# Then, if either the [[half-carry flag]] is set, or the lower nibble of the accumulator exceeds 0x09, add 0x06 to the accumulator.  This corrects the ones column and possibly increments the tens column by one.


DAA assumes the value in the accumulator is encoded in binary/hexadecimal because that is what the [[ADC (SPC700)|ADC]] command outputs.  Afterwards, the accumulator value will be in BCD.  The SPC700 has no [[decimal mode]], so that is why this command is important when working with decimal data.
DAA assumes the value in the accumulator is encoded in binary/hexadecimal (with any value in the range $00 to $FF) because that is what the [[ADC (SPC700)|ADC]] command can output.  Afterwards, the accumulator value will be in BCD where both nybbles are in the range 0 to 9.  The SPC700 has no [[decimal mode]], so that is why this command is important when working with decimal data.


==== Syntax ====
==== Syntax ====

Revision as of 20:57, 20 September 2024

Basic Info
Addressing Mode Opcode Length Speed
Accumulator DF 1 byte 3 cycles
Flags Affected
N V P B H I Z C
N . . . . . Z C

DAA (Decimal Adjust for Addition) is an SPC700 instruction that corrects a BCD sum:

  1. If either the carry flag is set or the accumulator exceeds 0x99, add 0x60 to the accumulator and set the carry flag. This corrects the tens column (but perhaps not completely).
  2. Then, if either the half-carry flag is set, or the lower nibble of the accumulator exceeds 0x09, add 0x06 to the accumulator. This corrects the ones column and possibly increments the tens column by one.

DAA assumes the value in the accumulator is encoded in binary/hexadecimal (with any value in the range $00 to $FF) because that is what the ADC command can output. Afterwards, the accumulator value will be in BCD where both nybbles are in the range 0 to 9. The SPC700 has no decimal mode, so that is why this command is important when working with decimal data.

Syntax

DAA
DAA A

See Also

External Links