Zilog Z80380 - Manual (Page 27)

4-2
Z380 ™
U SER ' S M ANUAL
DC-8297-03
Z ILOG
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.
A
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
register
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