Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
CPU Registers
3.3.1 Accumulator
The accumulator (A) shown in Figure 3-2 is a general-purpose 8-bit
register. The CPU uses the accumulator to hold operands and results of
arithmetic and non-arithmetic operations.
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
Unaffected by reset
Figure 3-2. Accumulator (A)
3.3.2 Index Register
In the indexed addressing modes, the CPU uses the byte in the index
register (X) shown in Figure 3-3 to determine the conditional address of
the operand. See 12.3.5 Indexed, No Offset, 12.3.6 Indexed, 8-Bit
Offset, and 12.3.7 Indexed, 16-Bit Offset for more information on
indexed addressing.
The 8-bit index register also can serve as a temporary data storage
location.
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
Unaffected by reset
Figure 3-3. Index Register (X)
MC68HC705C8A — Rev. 3
MOTOROLA
Technical Data
Central Processor Unit (CPU)
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