mc68hc05jp6pe Freescale Semiconductor, Inc, mc68hc05jp6pe Datasheet - Page 41

• Manufacturer Part Number: mc68hc05jp6pe
• Description: M68hc05 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

3.4 Index Register
3.5 Stack Pointer
MC68HC05JJ6/MC68HC05JP6
Freescale Semiconductor
Reset:
The index register is a general-purpose 8-bit register as shown in
3-3. 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 as shown in
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 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.
Read:
Write:
Reset:
Read:
Write:
—
Rev. 3.2
Bit
15
0
0
Bit 7
14
0
0
Central Processor Unit (CPU)
13
0
0
6
12
Figure 3-4. Stack Pointer (SP)
0
0
Figure 3-3. Index Register (X)
11
0
0
5
10
0
0
Unaffected by Reset
9
0
0
Figure
4
8
0
0
7
1
1
3-4. During a reset or after the
3
6
1
1
General Release Specification
Central Processor Unit (CPU)
5
1
2
4
1
3
1
1
2
1
Figure
1
1
Bit 0
Bit
0
1
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