Zilog Z80380 Manual do Utilizador descarregar pdf (Página 27)

4-2

Z380

™

USER'S MANUAL

DC-8297-03

ZILOG

4.2.2 Immediate (IM) (Continued)

Instruction

OPERATION

OPERAND

The operand value is in the instruction

Immediate mode is often used to initialize registers. Also,

this addressing mode is affected by the DDIR Immediate

Data Directives to expand the immediate value to 24 bits

or 32 bits.

Example of IM mode:

1. Load immediate value into accumulator

LD A,55H ;Load hex 55 into the accumulator.

Before instruction execution 12

After instruction execution 55

4.2.3 Indirect Register (IR)

In Indirect Register addressing mode, the register speci-

fied in the instruction holds the address of the operand.

The data to be processed is in the location specified by the

BC, DE, or HL register (depending on the instruction) for

memory accesses, or C register for I/O.

Memory or

Instruction Register I/O Port

OPERATION REGISTER → Address → OPERAND

The operand value is the contents of the location whose address is in the register.

Depending on the instruction, the operand specified by IR

mode is located in either the I/O address space (I/O

instruction) or memory address space (all other instruc-

tions).

Indirect Register mode can save space and reduce ex-

ecution time when consecutive locations are referenced or

one location is repeatedly accessed. This mode can also

be used to simulate more complex addressing modes,

since addresses can be computed before data is ac-

cessed.

The address in this mode is always treated as a 32-bit

mode. After reset, the contents of the extend registers

(registers with “z” suffix) are initialized as 0's; hence, these

instructions will be executed just as for the Z80/Z180.

Example of IR mode:

1. Load accumulator from the contents of memory

pointed by (HL)

LD A, (HL) ;Load the accumulator with the data

;addressed by the contents of HL

A HLz,HL

Before instruction

execution 0F 12345678

After instruction

execution 0B 12345678

Memory location 12345678 0B

2. Load 24-bit immediate value into HL

DDIR IB, LW ;next instruction is in Long Word

mode, with ;an additional

immediate data

LD HL, 123456H ;load HLz, and HL with constant

123456H

This case, the Z380 CPU appends 00H as a MSB byte.

HLz HL

Before instruction execution 0987 6543

After instruction execution 0012 3456

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 267 268

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