MC68HC908MR8 Datasheet, PDF (73/372 Pages) Motorola, Inc – Microcontrollers

Central Processor Unit (CPU)
CPU Registers
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.
Read:
Write:
Re-
set:
Bit 7
6
5
4
3
2
Unaffected by reset
Figure 6-2. Accumulator (A)
1
Bit 0
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.
In the indexed addressing modes, the CPU uses the contents of the
index register to determine the conditional address of the operand.
Bit
Bit
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Read:
Write:
Re-
set:
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)
The index register can serve also as a temporary data storage location.
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor
Central Processor Unit (CPU)
Technical Data
73