ZiLOG Z8 Technical Manual

External Interface (Z8681,Z8682)
7.8 INSTRUCTION TIMING
The high throughput of the Z8681/82 is due, in
part, to the use of instruction pipelining, in
which the instruction fetch and execution cycles
are overlapped. During the execution of the cur-
rent instruction the opcode of the next instruc-
tion is fetched as illustrated in Figure 6-10.
Figures 6-11 and 6-12 show typical instruction
cycle timing for instructions fetched from mem-
ory. For those instructions that require execu-
tion time longer than that of the overlapped
fetch, or reference program or data memory as part
of their execution, the pipe must be flushed. In
order to calculate the execution time of a pro-
gram, the internal clock periods shown in the
cycles column of the instruction formats in Sec-
tion 5.6 should be added together. The cycles are
equal to one-half the crystal or input clock rate.
7.9 Z8681 RESET CONDITIONS
After a hardware reset, Port 0 is configured as
input port, extended timing is set to accommodate
slow memory access during the configuration
routine, DM is inactive, and the stack resides in
the register file. Figure 7-10 shows the binary
values reset into P01M.
7.10 Z8682 RESET CONDITIONS
A fter a hardware reset, Port 0 is configured as
address lines A8-A1S' memory timing is normal, DM
is inactive, and the stack resides in the register
file. Figure 7-11 shows the binary values reset
into P01M.
R248 P01M
Port 0-1 Mode Register
(% F8; Write Only)
PO
C
-P0
7
MODE:]
OUTPUT = 00
INPUT
= 01
A
12
-A
15
= 1X -
EXTERNAL
MEMORY TIMING
NORMAL
= 0
·EXTENDED
= 1
c:
POO-P03 MODE
L 00 = OUTPUT
01 = INPUT
1X = As-All
STACK SELECTION
o = EXTERNAL
1
= INTERNAL
"ALWAYS EXTENDED TIMING AFTER RESET EXCEPT Z8682
figure 7-10. Z8681 Port 0 and 1 Reset Conditions
R248 P01M
Port 0-1 Mode Register
(% F8; Write Only)
PO
C
-P0
7
MODE:]
OUTPUT = 00
INPUT
= 01
A
12
-A
15
= 1X
EXTERNAL
MEMORY TIMING
NORMAL
= 0
I [ P"8o~' ~J'T~~T
01 = INPUT
1X = As-All
STACK SELECTION
o = EXTERNAL
EXTENDED
= 1
1
= INTERNAL
P1
o
-P1
7
MODE
'------- 10 = ADo-AD7
figure 7-11. Z8682 Ports 0 and 1 Reset Conditions
7-6 3047-008,3047-054

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English