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Z80 CPU Instructions UM008007-0715

Z80 CPU

User Manual

Descriptions of the General-Purpose Arithmetic and CPU Control Groups instructions

begin on page 170.

The decimal adjust instruction can adjust for subtraction and addition, making BCD arith-

metic operations simple.

1. To allow for this operation, the N flag is used. This flag is set if the most recent arithmetic

operation was a Subtract. The Negate Accumulator (NEG) instruction forms the two’s

complement of the number in the Accumulator.

2. A Reset Carry instruction is not included in the Z80 CPU, because this operation can

be easily achieved through other instructions such as a logical AND of the Accumu-

lator with itself.

Table 11 lists all of the 16-bit arithmetic operations between 16-bit registers. There are

five groups of instructions, including the Add with Carry and Subtract with Carry instruc-

tions; ADC and SBC affect all of the flags. These two groups simplify address calculation

or other 16-bit arithmetic operations.

Descriptions of the 16-Bit Arithmetic Group instructions begin on page 185.

Table 12. 16-Bit Arithmetic

Source

BC DE HL SP IX IY

Destination HL 09 19 29 39

Add (ADD)

Add with Carry and set ADC flags HL

Subtract with Carry and set SBC flags HL

Increment (INC) 03 13 23 33

Decrement (DEC) DB 1B 2B 3B

Note:

Notes:

Note:

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