M68ICS08GR datasheet(285/408 Pages) FREESCALE

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System Integration Module (SIM)

Exception Control

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

System Integration Module (SIM)

285

condition code register) and if the corresponding interrupt enable bit is

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 19-11

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 19-11

. 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

#$FF

PSHH

INT1 INTERRUPT SERVICE ROUTINE

PULH

RTI

PSHH

INT2 INTERRUPT SERVICE ROUTINE

ROUTINE

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