mc68hc05pv8a Freescale Semiconductor, Inc, mc68hc05pv8a Datasheet - Page 45

• Manufacturer Part Number: mc68hc05pv8a
• Description: Mc68hc05pv8a Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

3.2.2 Index Register
3.2.3 Stack Pointer
MC68HC(8)05PV8/A — Rev. 1.9
Reset
Reset:
Bit 15 14
0
0
In the indexed addressing modes, the CPU uses the byte in the index
register to determine the conditional address of the operand.
The 8-bit index register can also serve as a temporary data storage
location.
The stack pointer 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
(RSP) instruction, the stack pointer is preset 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 ten most significant bits of the stack pointer are permanently fixed
at 000000011, 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.
Bit 7
Freescale Semiconductor, Inc.
0
0
For More Information On This Product,
13
0
0
6
12
0
0
CPU and Instruction Set
Go to: www.freescale.com
Figure 3-3 Index Register
11
Figure 3-4 Stack Pointer
0
0
5
10
0
0
9
0
0
Unaffected by reset
4
8
0
0
7
1
1
3
6
1
1
5
1
2
4
1
CPU and Instruction Set
3
1
1
CPU Registers
Technical Data
2
1
1
1
Bit 0
Bit 0
1