MC68HC908AT32 Datasheet, PDF (86/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

System Integration Module (SIM)
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.
CLI
LDA #$FF
BACKGROUND
ROUTINE
INT1
PSHH
PULH
RTI
INT1 INTERRUPT SERVICE ROUTINE
INT2
PSHH
INT2 INTERRUPT SERVICE ROUTINE
PULH
RTI
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 M68HC05, M6805 and M146805
Families, 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.
7.5.1.2 SWI Instruction
The SWI instruction is a non-maskable instruction that causes an interrupt regardless of the state of the
interrupt mask (I bit) in the condition code register.
NOTE
A software interrupt pushes PC onto the stack. A software interrupt does
not push PC – 1, as a hardware interrupt does.
7.5.2 Reset
All reset sources always have higher priority than interrupts and cannot be arbitrated.
7.5.3 Break Interrupts
The break module can stop normal program flow at a software-programmable break point by asserting its
break interrupt output. (See Chapter 11 Break Module (BRK).) The SIM puts the CPU into the break state
MC68HC908AT32 Data Sheet, Rev. 3.1
86
Freescale Semiconductor