Operating Modes
Internal Resource Mapping
68HC(9)12DG128 Rev 1.0
MOTOROLA
Operating Modes
67
9-modes
Register Block
Mapping
After reset the 1K byte register block resides at location $0000 but can
be reassigned to any 2K byte boundary within the standard 64K byte
address space. Mapping of internal registers is controlled by five bits in
the INITRG register. The register block occupies the first 1K byte bytes
of the 2K byte block.
REG[15:11] — Internal register map position
These bits specify the upper five bits of the 16-bit registers address.
Normal modes: write once; special modes: write anytime. Read
anytime.
MMSWAI — Memory Mapping Interface Stop in Wait Control
This bit controls access to the memory mapping interface when in
Wait mode.
Normal modes: write anytime; special modes: write never. Read
anytime.
0 = Memory mapping interface continues to function during Wait
mode.
1 = Memory mapping interface access is shut down during Wait
mode.
RAM Mapping
The 68HC(9)12DG128 has 8K bytes of fully static RAM that is used for
storing instructions, variables, and temporary data during program
execution. Since the RAM is actually implemented with two 4K RAM
arrays, any misaligned word access between last address of first 4K
RAM and first address of second 4K RAM will take two cycles instead of
one. After reset, RAM addressing begins at location $2000 but can be
assigned to any 8K byte boundary within the standard 64K byte address
space. Mapping of internal RAM is controlled by three bits in the INITRM
register.
INITRG
— Initialization of Internal Register Position Register
$0011
Bit 7
6
5
4
3
2
1
Bit 0
REG15
REG14
REG13
REG12
REG11
0
0
MMSWAI
RESET:
0
0
0
0
0
0
0
0