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Architectural Overview UM008007-0715

Z80 CPU

User Manual

isters are used for a wide range of applications. They also simplify programing, specifi-

cally in ROM-based systems in which little external read/write memory is available.

Arithmetic Logic Unit

The 8-bit arithmetic and logical instructions of the CPU are executed in the Arithmetic

Logic Unit (ALU). Internally, the ALU communicates with the registers and the external

data bus by using the internal data bus. Functions performed by the ALU include:

• Add

• Subtract

• Logical AND

• Logical OR

• Logical exclusive OR

• Compare

• Left or right shifts or rotates (arithmetic and logical)

• Increment

• Decrement

• Set bit

• Reset bit

• Test bit

Instruction Register and CPU Control

As each instruction is fetched from memory, it is placed in the Instruction Register and

decoded. The control sections performs this function and then generates and supplies the

control signals necessary to read or write data from or to the registers, control the ALU,

and provide required external control signals.

Pin Description

The Z80 CPU I/O pins are shown in Figure 3. The function of each pin is described in the

section that follows.

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Zilog Z08470 Bedienungsanleitung Seite 16