MC68HC908GT16 Datasheet, PDF (77/412 Pages) Motorola, Inc – Microcontrollers

4.4 Interrupts
4.4.1 Effects
Resets and Interrupts
Interrupts
An interrupt temporarily changes the sequence of program execution to
respond to a particular event. An interrupt does not stop the operation of
the instruction being executed, but begins when the current instruction
completes its operation.
An interrupt:
• Saves the CPU registers on the stack. At the end of the interrupt,
the RTI instruction recovers the CPU registers from the stack so
that normal processing can resume.
• Sets the interrupt mask (I bit) to prevent additional interrupts.
Once an interrupt is latched, no other interrupt can take
precedence, regardless of its priority.
• Loads the program counter with a user-defined vector address
5
4
STACKING ³
ORDER ₂
1
•
•
•
CONDITION CODE REGISTER
ACCUMULATOR
INDEX REGISTER (LOW BYTE)*
PROGRAM COUNTER (HIGH BYTE)
PROGRAM COUNTER (LOW BYTE)
•
•
•
1
2
3 _UNSTACKING
4
ORDER
5
*High byte of index register is not stacked.
$00FF DEFAULT ADDRESS ON RESET
Figure 4-4. Interrupt Stacking Order
MC68HC908GT16 • MC68HC908GT8 — Rev. 2
MOTOROLA
Resets and Interrupts
Technical Data
77