MC68HC05P18A Datasheet, PDF (35/130 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
CPU Registers
3.3.1 Accumulator
The accumulator (A) is a general-purpose 8-bit register. The CPU uses
the accumulator to hold operands and results of arithmetic and non-
arithmetic operations.
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
Unaffected by reset
Figure 3-2. Accumulator (A)
1
Bit 0
3.3.2 Index Register
In the indexed addressing modes, the CPU uses the byte in the index
register (X) to determine the conditional address of the operand.
The 8-bit index register can also serve as a temporary data storage
location.
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
Unaffected by reset
Figure 3-3. Index Register (X)
1
Bit 0
3.3.3 Stack Pointer
The stack pointer (SP) is a 16-bit register that contains the address of
the next location on the stack. During a reset or after the reset stack
pointer (RSP) instruction, the stack pointer is preset to $00FF. The
address in the stack pointer decrements as data is pushed onto the
stack and increments as data is pulled from the stack.
MC68HC05P18A
Central Processor Unit (CPU)
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Technical Data