Program Memory - ZiLOG Z8 PLUS User Manual

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PROGRAM MEMORY

The program memory map is shown in Figure 1-6. The first two bytes of program memory are reserved for
the PC rollover vector. When the PC wraps around to 0000H, bytes 0000H and 0001H are executed as
instructions, enabling a user defined behavior for this occurrence. For example, a JR instruction in 0000H
and a corresponding displacement in 0001H could be defined for the PC rollover vector. The next 30 bytes
of Program Memory are reserved for the interrupt vectors. These locations contain 16-bit vectors that corre-
spond to the available interrupts. Address 0020H through the end of the populated memory (0FFFFh, 64 KB
maximum) consists of on-chip mask-programmable ROM or EPROM or Flash. The first byte of program
memory executed following a RESET is located at 0020H. See the product data sheet for the exact program,
data, register memory size, and address range available.
The internal program memory may be one-time programmable (OTP) or mask programmable dependent on
the specific device. A ROM protect feature prevents dumping of the ROM contents. The ROM Protect option
is mask-programmable and is selected by the customer when the ROM code is submitted. For programmable
memory devices, the ROM Protect option is an OTP programming option.