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4-1

Z380

™

USER'S MANUAL

ZILOG

DC-8297-03

4.1 INSTRUCTION

SER

’s M

ANUAL

CHAPTER 4

ADDRESSING MODES AND DATA TYPES

An instruction is a consecutive list of one or more bytes in

memory. Most instructions act upon some data; the term

operand refers to the data to be operated upon. For Z380

™

CPU instructions, operands can reside in CPU registers,

memory locations, or I/O ports (internal or external). The

method used to designate the location of the operands for

an instruction are called addressing modes. The Z380

CPU supports seven addressing modes; Register, Imme-

diate, Indirect Register, Direct Address, Indexed, Program

Counter Relative Address, and Stack Pointer Relative. A

wide variety of data types can be accessed using these

addressing modes.

4.2 ADDRESSING MODE DESCRIPTIONS

The following pages contain descriptions of the address-

ing modes for the Z380 CPU. Each description explains

how the operand’s location is calculated, indicates which

address spaces can be accessed with that particular

addressing mode, and gives an example of an instruction

using that mode, illustrating the assembly language format

for the addressing modes.

4.2.1 Register (R, RX)

When this addressing mode is used, the instruction pro-

cesses data taken from one of the 8-bit registers A, B, C,

D, E, H, L, IXU, IXL, IYU, IYL, one of the 16-bit registers BC,

DE, HL, IX, IY, SP, or one of the special byte registers I or

Storing data in a register allows shorter instructions and

faster execution that occur with instructions that access

memory.

Instruction

OPERATION REGISTER → OPERAND

The operand value is the contents of the register.

The operand is always in the register address space. The

opcode. In the case of Long Word register operation, it is

specified either through the SETC LW instruction or the

DDIR LW decoder directive.

Example of R mode:

1. Load register in Word mode.

DDIR W ;Next instruction in Word mode

LD BC,HL ;Load the contents of HL into BC

BCz BC HLz HL

Before instruction

execution 1234 5678 9ABC DEF0

After instruction

execution 1234 DEF0 9ABC DEF0

2. Load register in Long Word mode.

DDIR LW ;Next instruction in Long Word mode

LD BC,HL ;Load the contents of HL into BC

BCz BC HLz HL

Before instruction

execution 1234 5678 9ABC DEF0

After instruction

execution 9ABC DEF0 9ABC DEF0

4.2.2 Immediate (IM)

When the Immediate addressing mode is used, the data

processed is in the instruction.

The Immediate addressing mode is the only mode that

does not indicate a register or memory address as the

source operand.

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