MC68HC705K1 Datasheet, PDF (34/140 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
3.3.3 Stack Pointer
The stack pointer (SP) shown in Figure 3-4 is a 16-bit register that
contains the address of the next free location on the stack. During a
reset or after the reset stack pointer (RSP) instruction, the stack pointer
initializes 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.
The 11 most significant bits of the stack pointer are fixed permanently at
00000000111, so the stack pointer produces addresses from $00E0 to
$00FF. If subroutines and interrupts use more than 32 stack locations,
the stack pointer wraps around to address $00FF and begins writing
over the previously stored data. A subroutine uses two stack locations.
An interrupt uses five locations.
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 1
Write:
Reset: 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
= Unimplemented
Figure 3-4. Stack Pointer (SP)
Technical Data
Central Processor Unit (CPU)
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MC68HC705K1 — Rev. 2.0