ZiLOG Z8 Technical Manual

B.1 RESET
This section describes ZB reset conditions, reset
timing, and register initialization procedures.
A system reset overrides all other operating con-
ditions and puts the ZB into a known state. To
initialize the chip's internal logic, the reset
input must be held Low for at least 1 B clock
periods.
While RESET is Low, AS is output at the internal
Chapter 8
Reset and Clock
clock rate (XTAL frequency divided by 2), OS is
forced Low and R/W remains High. (Zilog Z-BUS com-
patible peripherals use the AS and 55 coincident
Low state as a peripheral reset function.) In
addition, interrupts are disabled, Ports 0, 1, and
2
are put in input mode, and %C is loaded into the
Program Counter.
The hardware Reset initializes the control and
peripheral registers, as shown in Table B.1.
Specific reset values are shown by 1s or as, while
bits whose states are unknown are indicated by the
Table B-1. Control and Peripheral Register Reset Values
Register
%FO Serial I/O
%F1
Timer Mode
%F2
Counter/Timer
%F3
f1 Prescaler
%F4
Counter/Timer
a
%F5
TO Prescaler
%F6
Port 2
Mode
%F7 Port
3 Mode
%F8 Port 0-1
Mode
ZB601/ZB611
%FB Port
0-1
Mode
ZB6B1
%F8 Port
0-1 Mode
Z8682
%F9
Interrupt Priority
%FA
Interrupt Request
%FB
Interrupt Mask
%FC
Flags
%FD
Register Pointer
%FE
Stack
Pointer
%FF
Stack Pointer
DJ 06 05 04 DJ 02 D1 Do
undefined
0 0 a 0 0 0 a
0
undefined
u u
u u
u u
a
0
undefined
u u u u
u u
u
0
a 0 0 a
a a
u
a
a 1 a
0
a a
a
0 0 a 0
undefined
u u a
0
0 0
a
a
a
u u
u
u u u u
undefined
undefined
undefined
undefined
COIIIIIents
Counter/Timers stopped
Single Pass count mode,
external clock source
Single Pass count mode
All lines input
Port 2 open-drain
P3
0
-P3
3
input; P34-P37 output
Ports a and 1 inputs; internal stack;
extended external memory timing
Port 0 inputs
Port 1 Address/Data; internal stack;
extended external memory timing
Port 0 Address
Port 1 Address/Data
internal stack; normal external
memory timing
Reset
all interrupt disabled
Interrupts disabled
Most significant byte
Least significant byte
8-1

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English