eZ80
®
CPU
User Manual
UM007714-0908 CPU Instruction Set
129
DAA
Decimal Adjust Accumulator
Operation
A ← Decimal Adjust (A)
Description
This instruction conditionally adjusts the accumulator, A, following addition and subtrac-
tion operations on binary-coded-decimal (BCD) values. For addition (
ADD
,
ADC
,
INC
)
or subtraction (
SUB
,
SBC
,
DEC
,
NEG
), Table 51 indicates the operation performed by
the
DAA
instruction.
Condition Bits Affected
Table 51. Operations of the DAA Instruction
Operation
C Before
DAA
Hex
Value in
Upper
Digit
(Bits 7:4)
H Before
DAA
Hex
Value in
Lower
Digit
(Bits 3:0)
Number
Added to
Byte
C After
DAA
H After
DAA
ADD, ADC,
or INC
0 0–9 0 0–9 00 0 0
00–80A–F0601
0 0–9 1 0–3 06 0 0
0 A–F 0 0–9 60 1 0
09–F0A–F6611
0 A–F 1 0–3 66 1 0
1 0–2 0 0–9 60 1 0
10–20A–F6611
1 0–3 1 0–3 66 1 0
SUB, SBC,
DEC, or
NEG
0 0–9 0 0–9 00 0 0
00–816–FFA00
17–F00–9A010
1 6–F 1 6–F 9A 1 0
S Set if the msb of the result is 1 after the operation; reset
otherwise.
Z Set if result is 0; reset otherwise.
H See
Table 51.
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