MC68HC05C8A Datasheet, PDF (21/116 Pages) Motorola, Inc – Microcontrollers

Chapter 2
Memory
2.1 Introduction
The MC68HC05C8A has an 8-Kbyte memory map, consisting of user read-only memory (ROM), user
random-access memory (RAM), self-check ROM, and input/output (I/O) registers. See Figure 2-1 and
Figure 2-2.
2.2 Read-Only Memory (ROM)
The user ROM consists of 48 bytes of page zero ROM from $0020 to $004F, 7680 bytes of user ROM
from $0100 to $1EFF, and 16 bytes of user vectors from $1FF0 to $1FFF. The self-check ROM and
vectors are located from $1F00 to $1FEF. See Figure 2-1.
Twelve of the user vectors, $1FF4–$1FFF, are dedicated to user-defined reset and interrupt vectors. The
remaining four bytes from $1FF0–$1FF3 are not used.
2.3 ROM Security Feature
A security⁽¹⁾ feature has been incorporated into the MC68HC05C8A to help prevent externally reading of
code in the ROM. This feature aids in keeping customer developed software proprietary.
2.4 Random-Access Memory (RAM)
The user RAM consists of 176 bytes and is used both for general-purpose RAM and stack area. The stack
begins at address $00FF. The stack pointer can access 64 bytes of RAM in the range $00FF to $00C0.
See Figure 2-1.
NOTE
Using the stack area for data storage or temporary work locations requires
care to prevent it from being overwritten due to stacking from an interrupt
or subroutine call.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the ROM difficult for
unauthorized users.
MC68HC05C8A • MC68HCL05C8A • MC68HSC05C8A Data Sheet, Rev. 5.1
Freescale Semiconductor
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