mc68hc912bl16 Freescale Semiconductor, Inc, mc68hc912bl16 Datasheet - Page 28

• Manufacturer Part Number: mc68hc912bl16
• Description: 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

EME — Emulate Port E
5.3 Internal Resource Mapping
5.3.1 Register Block Mapping
INITRG — Initialization of Internal Register Position Register
REG[15:11] — Internal register map position
MMSWAI — Memory Mapping Interface Stop in Wait Control
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RESET:
Removing the registers from the map allows the user to emulate the function of these registers exter-
nally. In single-chip mode PORTE and DDRE are always in the map regardless of the state of this bit.
Normal modes: write once; special modes: write anytime EXCEPT the first time. Read anytime.
The internal register block, RAM, Flash EEPROM and EEPROM have default locations within the 64-
Kbyte standard address space but may be reassigned to other locations during program execution by
setting bits in mapping registers INITRG, INITRM, and INITEE. During normal operating modes these
registers can be written once. It is advisable to explicitly establish these resource locations during the
initialization phase of program execution, even if default values are chosen, in order to protect the reg-
isters from inadvertent modification later.
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 fol-
lowed with a NOP instruction.
If conflicts occur when mapping resources, the register block will take precedence over the other re-
sources; RAM, Flash EEPROM, or EEPROM addresses occupied by the register block will not be avail-
able for storage. When active, BDM ROM takes precedence over other resources although a conflict
between BDM ROM and register space is not possible. Table 10 shows resource mapping precedence.
In expanded modes, all address space not utilized by internal resources is by default external memory.
After reset the 512 byte register block resides at location $0000 but can be reassigned to any 2-Kbyte
boundary within the standard 64-Kbyte address space. Mapping of internal registers is controlled by five
bits in the INITRG register. The register block occupies the first 512 bytes of the 2-Kbyte block.
These bits specify the upper five bits of the 16-bit registers address.
Write once in normal modes or anytime in special modes. Read anytime.
This bit controls access to the memory mapping interface when in Wait mode.
0 = PORTE and DDRE are in the memory map.
1 = PORTE and DDRE are removed from the internal memory map (expanded mode).
REG15
Bit 7
0
REG14
6
0
Freescale Semiconductor, Inc.
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Precedence
REG13
1
2
3
4
5
6
5
0
Table 10 Mapping Precedence
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REG12
4
0
BDM ROM (if active)
External Memory
Flash EEPROM
Register Space
Resource
REG11
EEPROM
RAM
3
0
2
0
0
1
0
0
MC68HC912BL16TS/D
MMSWAI
MC68HC912BL16
Bit 0
0
$0011