MC68HC908GR16 Datasheet, PDF (90/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
7.3 CPU Registers
Figure 7-1 shows the five CPU registers. CPU registers are not part of the memory
map.
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 7-1. CPU Registers
7.3.1 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 7-2. Accumulator (A)
1
Bit 0
7.3.2 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.
Data Sheet
90
Central Processor Unit (CPU)
For More Information On This Product,
Go to: www.freescale.com
MC68HC908GR16 — Rev. 1.0
MOTOROLA