MC68HC705P9 Datasheet, PDF (37/156 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Accumulator
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 2. 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 3. Index Register (X)
1
Bit 0
Stack Pointer
5-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 4. Stack Pointer (SP)
CPU
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