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S3F80JB INSTRUCTION SET
6-33
DA — Decimal Adjust
DA dst
Operation: dst ← DA dst
The destination operand is adjusted to form two 4-bit BCD digits following an addition or
subtraction operation. For addition (ADD, ADC) or subtraction (SUB, SBC), the following table
indicates the operation performed. (The operation is undefined if the destination operand was not
the result of a valid addition or subtraction of BCD digits):
Instruction Carry
Before DA
Bits 4–7
Value (Hex)
H Flag
Before DA
Bits 0–3
Value (Hex)
Number Added
to Byte
Carry
After DA
0 0–9 0 0–9 00 0
0 0–8 0 A–F 06 0
0 0–9 1 0–3 06 0
ADD 0 A–F 0 0–9 60 1
ADC 0 9–F 0 A–F 66 1
0 A–F 1 0–3 66 1
1 0–2 0 0–9 60 1
1 0–2 0 A–F 66 1
1 0–3 1 0–3 66 1
0 0–9 0 0–9 00 = – 00 0
SUB 0 0–8 1 6–F FA = – 06 0
SBC 1 7–F 0 0–9 A0 = – 60 1
1 6–F 1 6–F 9A = – 66 1
Flags: C: Set if there was a carry from the most significant bit; cleared otherwise (see table).
Z: Set if result is "0"; cleared otherwise.
S: Set if result bit 7 is set; cleared otherwise.
V: Undefined.
D: Unaffected.
H: Unaffected.
Format:
Bytes Cycles Opcode
(Hex)
Addr Mode
dst
opc dst
2 4 40 R
4 41 IR