MC68HC908KX8 Datasheet, PDF (62/310 Pages) Motorola, Inc – Microcontrollers

Central Processor Unit (CPU)
5.4.3 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, the stack pointer is preset
to $00FF. The reset stack pointer (RSP) instruction sets the least
significant byte (LSB) to $FF and does not affect the most significant
byte (MSB). The stack pointer decrements as data is pushed onto the
stack and increments as data is pulled from the stack.
In the stack pointer 8-bit offset and 16-bit offset addressing modes, the
stack pointer can function as an index register to access data on the
stack. The CPU uses the contents of the stack pointer to determine the
conditional address of the operand.
Bit
Bit
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Read:
Write:
Reset: 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
Figure 5-4. Stack Pointer (SP)
NOTE:
The location of the stack is arbitrary and may be relocated anywhere in
the random-access memory (RAM). Moving the SP out of page 0 ($0000
to $00FF) frees direct address (page 0) space. For correct operation, the
stack pointer must point only to RAM locations.
Technical Data
62
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
Central Processor Unit (CPU)
MOTOROLA