Program Memory - ZiLOG Z8 User Manual

Z8 Microcontrollers
Address Space

2.5 PROGRAM MEMORY

The first 12 bytes of Program Memory are reserved for the inter-
rupt vectors (Figure 2-7). These locations contain six 16-bit vec-
tors that correspond to the six available interrupts. Address 12 up
to the maximum ROM address consists of on-chip mask-pro-
grammable ROM. See the product data sheet for the exact pro-
gram, data, register memory size, and address range available.
At addresses outside the internal ROM, the Z8 executes external
program memory fetches through Port 0 and Port 1 in Ad-
dress/Data mode for devices with Port 0 and Port 1 featured.
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).
2-10
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
Figure 2-7. Z8 Program Memory Map
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 selected
by the customer when the ROM code is submitted. For the OTP
ROM, the ROM Protect option is an OTP programming option.
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
ZiLOG
UM001601-0803