MC68HC05P1ADW FREESCALE [Freescale Semiconductor, Inc], MC68HC05P1ADW Datasheet - Page 33

• Manufacturer Part Number: MC68HC05P1ADW
• Description: General Release Specification
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

3.3.1 Accumulator
3.3.2 Index Register
3.3.3 Stack Pointer
MC68HC05P1A
—
Rev. 3.0
The accumulator (A) is a general-purpose 8-bit register used to hold
operands and results of arithmetic calculations or data manipulations.
The index register (X) is an 8-bit register used for the indexed
addressing value to create an effective address. The index register also
may be used as a temporary storage area.
In indexed addressing with no offset, the index register contains the low
byte of the operand address, and the high byte is assumed to be $00. In
indexed addressing with an 8-bit offset, the CPU finds the operand
address by adding the index register contents to an 8-bit immediate
value. In indexed addressing with a 16-bit offset, the CPU finds the
operand address by adding the index register contents to a 16-bit
immediate value.
The stack pointer (SP) contains the address of the next free location on
the stack. During an MCU reset or the reset stack pointer (RSP)
instruction, the stack pointer is set to location $00FF. The stack pointer
is then decremented as data is pushed onto the stack and incremented
as data is pulled from the stack.
When accessing memory, the eight most significant bits (MSB) are
permanently set to 00000011. These eight bits are appended to the six
least significant bits (LSB) to produce an address within the range of
$00FF to $00C0. Subroutines and interrupts may use up to 64 (decimal)
locations. If 64 locations are exceeded, the stack pointer wraps around
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CPU Core
7
7
A
X
General Release Specification
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CPU Registers
CPU Core