MC68HC705J1ACPE Datasheet, PDF (49/162 Pages) Freescale Semiconductor, Inc – Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.
Central Processor Unit (CPU)
CPU Registers
3.5.3 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 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 3-4. Stack Pointer (SP)
The 10 most significant bits of the stack pointer are permanently fixed at
0000000011, so the stack pointer produces addresses from $00C0 to
$00FF. If subroutines and interrupts use more than 64 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.
MC68HC705J1A — Rev. 4.0
Central Processor Unit (CPU)
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Technical Data