mc68hc908ap8a Freescale Semiconductor, Inc, mc68hc908ap8a Datasheet - Page 56

• Manufacturer Part Number: mc68hc908ap8a
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Central Processor Unit (CPU)
4.3 CPU Registers
Figure 4-1
4.3.1 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.
4.3.2 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.
56
shows the five CPU registers. CPU registers are not part of the memory map.
Reset:
Read:
Write:
15
15
15
Bit 7
H
MC68HC908AP A-Family Data Sheet, Rev. 3
6
Figure 4-2. Accumulator (A)
Figure 4-1. CPU Registers
V 1 1 H I N Z C
7
7
5
X
Unaffected by reset
4
0
0
0
0
0
CONDITION CODE REGISTER (CCR)
CARRY/BORROW FLAG
ZERO FLAG
NEGATIVE FLAG
INTERRUPT MASK
HALF-CARRY FLAG
TWO’S COMPLEMENT OVERFLOW FLAG
ACCUMULATOR (A)
INDEX REGISTER (H:X)
STACK POINTER (SP)
PROGRAM COUNTER (PC)
3
2
1
Freescale Semiconductor
Bit 0