MC68HC705P9 Datasheet, PDF (46/160 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
4.6 CPU Registers
The M68HC05 CPU contains five registers that control and monitor MCU
operation:
• Accumulator
• Index register
• Stack pointer
• Program counter
• Condition code register
CPU registers are not memory mapped.
4.6.1 Accumulator
The accumulator is a general-purpose 8-bit register. The CPU uses the
accumulator to hold operands and the results of arithmetic and logic
operations.
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
Unaffected by reset
Figure 4-2. Accumulator (A)
1
Bit 0
4.6.2 Index Register
The index register can be used for data storage or as a counter. In the
indexed addressing modes, the CPU uses the byte in the index register
to determine the effective address of the operand.
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
Unaffected by reset
Figure 4-3. Index Register (X)
1
Bit 0
Technical Data
46
Central Processor Unit (CPU)
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MC68HC705P9 — Rev. 4.0
MOTOROLA