Z8 Microcontrollers
Address Space
ZiLOG
2-10
UM001600-Z8X0599
2.5 PROGRAM MEMORY
The first 12 bytes of Program Memory are reserved for the
interrupt vectors (Figure 2-7). These locations contain six
16-bit vectors that correspond to the six available inter-
rupts. Address 12 up to the maximum ROM address con-
sists of on-chip mask-programmable ROM. See the prod-
uct data sheet for the exact program, data, register
memory size, and address range available. At addresses
outside the internal ROM, the Z8 executes external pro-
gram memory fetches through Port 0 and Port 1 in Ad-
dress/Data mode for devices with Port 0 and Port 1 fea-
tured. Otherwise, the program counter will continue to
execute NOPs up to address FFFFH, roll over to 0000H,
and continue to fetch executable code (Figure 2-7).
The internal program memory is one-time programmable
(OTP) or mask programmable dependent on the specific
device.
A ROM protect feature prevents dumping of the
ROM contents by inhibiting execution of the LDC, LDCI,
LDE, and LDEI instructions to Program Memory in all
modes. ROM look-up tables cannot be used with this
feature.
The ROM Protect option is mask-programmable, to be se-
lected by the customer when the ROM code is submitted.
For the OTP ROM, the ROM Protect option is an OTP pro-
gramming option.
Figure 2-7. Z8 Program Memory Map
Interrupt
Vector
(Upper Byte)
External
ROM and RAM
On - Chip
ROM
65535
IRQ
5
4096
4095
Interrupt
Vector
(Lower Byte)
Location of
First Byte of
Instruction
Executed
After RESET
IRQ
0
IRQ
0
IRQ
1
IRQ
1
IRQ
2
IRQ
2
IRQ
3
IRQ
3
IRQ
4
IRQ
4
IRQ
5
12
1
2
3
4
5
6
7
8
9
10
11
0