MC97F2664
96
April 11, 2014 Ver. 1.4
10.5 Interrupt Sequence
An interrupt request is held
until the interrupt is accepted or the interrupt latch is cleared to ‘0’ by a reset or an
instruction. Interrupt acceptance always generates at last cycle of the instruction. So instead of fetching the
current instruction, CPU executes internally LCALL instruction and saves the PC at stack. For the interrupt
service routine, the interrupt controller gives the address of LJMP instruction to CPU. Since the end of the
execution of current instruction, it needs 3~9 machine cycles to go to the interrupt service routine. The interrupt
service task is terminated by the interrupt return instruction [RETI]. Once an interrupt request is generated, the
following process is performed.
Figure 10.3 Interrupt Vector Address Table
Saves PC value in order to continue
process again after executing ISR
IE.EA Flag
0
1
Program Counter low Byte
SP
SP + 1
M(SP)
(PCL)
2
Program Counter high Byte
SP
SP + 1
M(SP)
(PCH)
3
Interrupt Vector Address occurrence
(Interrupt Vector Address)
4
ISR(Interrupt Service Routine) move,
execute
5
Return from ISR
RETI
6
Program Counter high Byte recovery
(PCH)
M(SP), SP
SP-1
7
Main Program execution
10
Program Counter low Byte recovery
(PCL)
M(SP), SP
SP-1
8
IE.EA Flag
1
9
Содержание MC97F2664
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