Motorola MC68HC908MR32 사용자 설명서
Central Processor Unit (CPU)
CPU Registers
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
Advance Information
MOTOROLA
Central Processor Unit (CPU)
73
6.4.1 Accumulator
The accumulator is a general-purpose 8-bit register. The CPU uses the
accumulator to hold operands and the results of arithmetic/logic
operations.
accumulator to hold operands and the results of arithmetic/logic
operations.
6.4.2 Index Register
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.
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.
index register to determine the conditional address of the operand.
The index register can serve also as a temporary data storage location.
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
Unaffected by reset
Figure 6-2. Accumulator (A)
Bit
15
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
Read:
Write:
Reset:
0
0
0
0
0
0
0
0
X
X
X
X
X
X
X
X
X = Indeterminate
Figure 6-3. Index Register (H:X)