MC68HC05P9A Datasheet, PDF (31/158 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Accumulator
Freescale Semiconductor, Inc.
CPU
CPU Registers
The accumulator is a general-purpose 8-bit register. The CPU uses the
accumulator to hold operands and the results of arithmetic and logic
operations.
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
Unaffected by reset
Figure 12. Accumulator (A)
1
Bit 0
Index Register
The index register can be used for data storage or as a counter. In the
indexed addressing modes, the CPU uses the byte in the index register
to determine the effective address of the operand.
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
Unaffected by reset
Figure 13. Index Register (X)
1
Bit 0
Stack Pointer
9-hc05cpu
MOTOROLA
The stack pointer is a 16-bit register that contains the address of the next
stack location to be used. During a reset or after the reset stack pointer
instruction (RSP), the stack pointer is preset to $00FF. The address in
the stack pointer decrements after a byte is stacked and increments
before a byte is unstacked.
Bit
Bit
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Read: 0 0 0 0 0 0 0 0 1 1
Write:
Reset: 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
= Unimplemented
Figure 14. Stack Pointer (SP)
CPU
31
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