MC68HC908RF2 Datasheet, PDF (67/254 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Central Processor Unit (CPU)
CPU Registers
15
H
15
15
7
0
ACCUMULATOR (A)
0
X
INDEX REGISTER (H:X)
0
STACK POINTER (SP)
0
PROGRAM COUNTER (PC)
7
0
V 1 1 H I N Z C CONDITION CODE REGISTER (CCR)
CARRY/BORROW FLAG
ZERO FLAG
NEGATIVE FLAG
INTERRUPT MASK
HALF-CARRY FLAG
TWO’S COMPLEMENT OVERFLOW FLAG
Figure 5-1. CPU Registers
5.4.1 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.
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
Unaffected by reset
Figure 5-2. Accumulator (A)
1
Bit 0
5.4.2 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.
MC68HC908RF2 — Rev. 1
MOTOROLA
Central Processor Unit (CPU)
Advance Information
67