Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
8.4.1 Accumulator (A)
The accumulator is a general-purpose 8-bit register. The CPU uses the
accumulator to hold operands and the results of arithmetic/logic
operations.
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
Unaffected by reset
Figure 8-2. Accumulator (A)
8.4.2 Index Register (H:X)
The 16-bit index register allows indexed addressing of a 64-Kbyte
memory space. H is the upper byte of the index register and X is the
lower byte. H:X is the concatenated 16-bit index register.
In the indexed addressing modes, the CPU uses the contents of the
index register to determine the conditional address of the operand.
Bit
Bit
0
15 14 13 12 11 10
9
0
8
0
7
6
5
4
3
2
1
Read:
Write:
Reset:
0
0
0
0
0
0
X
X
X
X
X
X
X
X
X = Indeterminate
Figure 8-3. Index Register (H:X)
The index register can also be used as a temporary data storage
location.
Technical Data
MC68HC908AS60 — Rev. 1.0
Central Processor Unit (CPU)
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