MC68HC812A4 Datasheet, PDF (84/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Operating Modes and Resource Mapping
Writes to the mapping registers go into effect between the cycle that
follows the write and the cycle after that. To assure that there are no
unintended operations, a write to one of these registers should be
followed with a NOP (no operation) instruction.
If conflicts occur when mapping resources, the register block takes
precedence over the other resources; RAM or EEPROM addresses
occupied by the register block are not available for storage. When active,
BDM ROM takes precedence over other resources although a conflict
between BDM ROM and register space is not possible. Table 5-2 shows
resource mapping precedence.
All address space not used by internal resources is external memory by
default.
The memory expansion module manages three memory overlay
windows:
1. Program
2. Data
3. One extra page overlay
The sizes and locations of the program and data overlay windows are
fixed. One of two locations can be selected for the extra page (EPAGE).
Table 5-2. Mapping Precedence
Precedence
1
2
3
4
5
Resource
BDM ROM (if active)
Register space
RAM
EEPROM
External memory
MC68HC812A4 — Rev. 3.0
84
Operating Modes and Resource Mapping
Advance Information
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