ZiLOG Z8 Technical Manual

Chapter 3
Address
Spaces
3.1 INTRODUCTION
DEC
255
Three address spaces are available in the Z8 254
microcomputer:
253
252
• The CPU Register rile contains addresses for 251
all general-purpose, peripheral, control, and 250
I/O port registers. 249
248
• The CPU Program Memory contains addresses for 247
all memory locations having executable code 246
and/or data. 245
244
• The CPU Data Memory contains addresses for all 243
memory locations that hold data only. 242
These address spaces are described in detail in
the following sections.
3.2 CPU REGISTER rILE
The register file totals 256 consecutive bytes, of
which 144 have been implemented. (Unused register
space is reserved for future expansion.) The reg-
ister file consists of 4 I/O ports (RO-R3), 124
general-purpose registers (R4-R127), 9 peripheral
registers (R240-R248), and 7 control registers
(R249-R255). Figure 3-1 shows the layout of the
register file, including register names, loca-
tions, and identifiers.
241
240
127
4
2
STACK POINTER (BITS 7-0)
STACK POINTER (BITS 15-8)
REGISTER POINTER
PROGRAM CONTROL FlAGS
INTERRUPT MASK REGISTER
INTERRUPT REOUEST REGISTER
INTERRUPT PRIORITY REGISTER
PORTS 0-1
MODE
PORT 3 MODE
PORT
2 MODE
TO PRESCALER
TIMER/COUNTER 0
T1 PRESCALER
TIMER/COUNTER 1
TIMER MODE
SERIAL I/O
NOT
IMPLEMENTED
GENERAL·PURPOSE
REGISTERS
PORT 3
PORT 2
PORT 1
PORT 0
HEX
FF
FE
FD
FC
FB
FA
F9
F8
F7
F6
F5
F4
F3
F2
F1
FO
7F
04
03
02
01
00
Figure 3-1. Register rile
L.._M_S_B_ ..... _L_S_B_.I1 n = EVEN ADDRESS
Rn
Rn+1
IDENTIFIERS
SPL
SPH
RP
FLAGS
IMR
IRO
IPR
P01M
P3M
P2M
PREO
TO
PRE1
T1
TMR
SIO
P3
P2
P1
PO
Registers can be accessed as either 8- or 16-bit
registers using Direct, Indirect, or Indexed
addressing. All 144 registers can be referenced
or modified by any instruction that accesses an
8-bit register, without the need for special
instructions. Registers accessed as 16-bits are
treated as even-odd register pairs (there are 72
valid pairs). In this case, the data I s MSB is
stored in the even-numbered register, while the
LSB goes into the next higher odd-numbered
register (Figure 3-2).
Figure 3-2. 16-Bit Register Addressing
2037-006, 3047-047
3-1

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English