MC68HC05P9A Datasheet, PDF (24/158 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Memory
Freescale Semiconductor, Inc.
RAM
The 128 addresses from $0080–$00FF are RAM locations. The CPU
uses the top 64 RAM addresses, $00C0–$00FF, as the stack. Before
processing an interrupt, the CPU uses five bytes of the stack to save the
contents of the CPU registers. During a subroutine call, the CPU uses
two bytes of the stack to store the return address. The stack pointer
decrements when the CPU stores a byte on the stack and increments
when the CPU retrieves a byte from the stack.
NOTE:
Be careful when using nested subroutines or multiple interrupt levels.
The CPU may overwrite data in the RAM during a subroutine or during
the interrupt stacking operation.
ROM
The following addresses are mask programmable ROM locations:
• $0020–$004F
• $0100–$08FF
• $1FF8–$1FFF (reserved for user-defined interrupt and reset
vectors)
ROM Security Feature
A security¹ feature has been incorporated into the MC68HC05P9A to
help prevent externally reading of code in the ROM. This feature aids in
keeping customer developed software proprietary.
1. No security feature is absolutely secure. However, Motorola’s strategy is to make reading or
copying the ROM difficult for unauthorized users.
10-mc68hc05p9a
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Memory
MOTOROLA
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