Z8 ® External Memory - ZiLOG Z8 Series User Manual

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Z8 External Memory
Z8 CPU, in some cases, has the capability to access external Program Memory with the
16-bit Program Counter. To access external Program Memory the Z8 CPU offers multi-
plexed address/data lines (AD7–AD0) on Port 1 and address lines (A15–A8) on Port 0.
This feature only applies to devices that offer Port 0 and Port 1. The maximum external
address is
Strobe), DS (Data Strobe), and R/W (Read/Write). The origin of the external Program
Memory starts after the last address of the internal ROM.
example of external Program Memory for the Z8 CPU.
UM001604-0108
65535
4096
4095
Location of
First Byte of
Instruction
Executed
After RESET
12
11
10
9
8
7
Interrupt
6
Vector
(Lower Byte)
5
4
Interrupt
3
Vector
(Upper Byte)
2
1
0
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Figure 8. Z8
. This memory interface is supported by the control lines AS (Address
FFFF
External
ROM and RAM
On–Chip
ROM
IRQ
5
IRQ
5
IRQ
4
IRQ
4
IRQ
3
IRQ
3
IRQ
2
IRQ
2
IRQ
1
IRQ
1
IRQ
0
IRQ
0
Program Memory Map
Z8
User Manual
Figure 9 on page 21 displays an
Address Space
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CPU
20