MC68HC705J1ACPE Datasheet, PDF (48/162 Pages) Freescale Semiconductor, Inc – Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
3.5 CPU Registers
The M68HC05 CPU contains five registers that control and monitor
microcontroller unit (MCU) operation:
• Accumulator
• Index register
• Stack pointer
• Program counter
• Condition code register
CPU registers are not memory mapped.
3.5.1 Accumulator
The accumulator (A) is a general-purpose 8-bit register. The CPU uses
the accumulator to hold operands and results of ALU operations.
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
Unaffected by reset
Figure 3-2. Accumulator (A)
1
Bit 0
3.5.2 Index Register
In the indexed addressing (X) modes, the CPU uses the byte in the index
register to determine the conditional address of the operand. The index
register also can serve as a temporary storage location or a counter.
Technical Data
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
Unaffected by reset
Figure 3-3. Index Register (X)
1
Bit 0
MC68HC705J1A — Rev. 4.0
Central Processor Unit (CPU)
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