MC68HC705K1 Datasheet, PDF (47/140 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Interrupts
Interrupt Processing
4.4 Interrupt Processing
The CPU does these things to begin servicing an interrupt:
• Stores the CPU registers on the stack in the order shown in
Figure 4-3
• Sets the I bit in the condition code register to prevent further
interrupts
• Loads the program counter with the contents of the appropriate
interrupt vector locations:
– $03FC and $03FD (software interrupt vector)
– $03FA and $03FB (external interrupt vector)
– $03F8 and $03F9 (timer interrupt vector)
The return-from-interrupt (RTI) instruction causes the CPU to recover
the CPU registers from the stack as shown in Figure 4-3.
UNSTACKING
•
ORDER
•
•
$00E0 (BOTTOM OF STACK)
$00E1
$00E2
•
•
•
5
1
4
2
3
3
2
4
1
5
CONDITION CODE REGISTER
ACCUMULATOR
INDEX REGISTER
PROGRAM COUNTER (HIGH BYTE)
PROGRAM COUNTER (LOW BYTE)
STACKING
ORDER
•
•
•
•
•
•
$00FD
$00FE
$00FF (TOP OF STACK)
Figure 4-3. Interrupt Stacking Order
MC68HC705K1 — Rev. 2.0
Interrupts
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Technical Data