MC68HC08LT8 Datasheet, PDF (126/156 Pages) Freescale Semiconductor, Inc – Microcontrollers

Central Processor Unit (CPU)
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 14-1. CPU Registers
14.3.1 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 14-2. Accumulator (A)
1
Bit 0
14.3.2 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.
The index register can serve also as a temporary data storage location.
Bit
Bit
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Read:
Write:
Reset: 0 0 0 0 0 0 0 0 X X X X X X X X
X = Indeterminate
Figure 14-3. Index Register (H:X)
MC68HC08LT8 Data Sheet, Rev. 1
126
Freescale Semiconductor