XC68HC705JJ7 Motorola, XC68HC705JJ7 Datasheet - Page 47

• Manufacturer Part Number: XC68HC705JJ7
• Description: MICROCONTROLLER
• Manufacturer: Motorola

3.4 Index Register
3.5 Stack Pointer
MC68HC705JJ7 • MC68HC705JP7 — REV 4
MOTOROLA
Reset:
The index register is a general-purpose 8-bit register as shown in
Figure
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:
Bit
15
0
0
3-3. In the indexed addressing modes, the CPU uses the byte in
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
9
0
0
Unaffected by reset
Figure
4
8
0
0
7
1
1
3-4. During a reset or after the
3
6
1
1
Central Processor Unit (CPU)
5
1
2
4
1
Advance Information
3
1
1
Index Register
2
1
1
1
Bit 0
Bit
0
1
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