ZiLOG Z8 Technical Manual

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4.1 INTRODUCTION
The Z8 microcomputer provides six addressing
modes:
•
Register (R)
•
Indirect Register
(IR)
•
Indexed (X)
•
Direct (D)
•
Relative (RA)
•
Immediate (It1)
With the exception of immediate data and condition
codes, all operands are expressed as register
file, program memory, or dat a memory addresses.
Registers are accessed using 8-bit addresses in
the range 0-127 and 240-255.
Working
registers are accessed using 4-bit
addresses in the range 0-15. The address of the
register being accessed is formed by the concate-
nation of the upper four bits in the Register
8·BIT REGISTER
FILE ADDRESS
PROGRAM MEMORY
Chapter 4
Address Modes
Pointer (R253) with the 4-bit working register
address supplied by the instruction.
Registers can be used in pairs to designate 16-bit
values or memory addresses. A register pair must
be
speci fied as an even-numbered address in the
range 0, 2, •••• , 14.
Addressing
modes are instruction-specific.
Section 5.4 discusses each addressing mode as it
corresponds to particular instructions.
In the following definitions,
"register" also implies register
register, or working register pair.
4.2 REGISTER ADDRESSING (R)
the use of
pair, working
In the Register addressing mode, the operand value
is the contents of the specified register or
register pair (Figures 4-1 and 4-2).
REGISTER FILE
P'
dst
OPERAND L
POINTS TO ONE REGISTER
OPCODE
/
ONE·OPERAND
INSTRUCTION
EXAMPLE
4·BIT WORKING
REGISTER
TWO·OPERAND
INSTRUCTION
EXAMPLE
,
'"
,
~
V
PROGRAM MEMORY
,
dst
I
src
.i
OPCODE
/
IN REGISTER FILE
VALUE USED IN
INSTRUCTION EXECUTION
Figure 4-1. Register Addressing
/
REGISTER FILE
RP
OPERAND
POINTS TO
THE
WORKING REGISTER
Figure 4-2. Working-Register Addressing
.. ~
)
/
POINTS TO
ORIGIN
OF
WORKING
REGISTER
GROUP
3047-056,3047-057 4-1

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English