Freescale Semiconductor MC68HC08KH12 - Manual (Page 75)

MC68HC(7)08KH12 — Rev. 1.1 Advance Information
Freescale Semiconductor 75
set, the SIM proceeds with interrupt processing; otherwise, the next
instruction is fetched and executed.
If more than one interrupt is pending at the end of an instruction
execution, the highest priority interrupt is serviced first.
Figure 7-11
demonstrates what happens when two interrupts are pending. If an
interrupt is pending upon exit from the original interrupt service routine,
the pending interrupt is serviced before the LDA instruction is executed.
Figure 7-11
.
Interrupt Recognition Example
The LDA opcode is prefetched by both the INT1 and INT2 RTI
instructions. However, in the case of the INT1 RTI prefetch, this is a
redundant operation.
NOTE: To maintain compatibility with the M6805 Family, the H register is not
pushed on the stack during interrupt entry. If the interrupt service routine
modifies the H register or uses the indexed addressing mode, software
should save the H register and then restore it prior to exiting the routine.
CLI
LDA
INT1
PULH
RTI
INT2
BACKGROUND ROUTINE #$FF
PSHH
INT1 INTERRUPT SERVICE ROUTINE
PULH
RTI
PSHH
INT2 INTERRUPT SERVICE ROUTINE