MC68HC908GR4MP datasheet(48/286 Pages) FREESCALE

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Resets and Interrupts

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

Freescale Semiconductor

After every instruction, the CPU checks all pending interrupts if the I bit is not set. If more than one

interrupt is pending when an instruction is done, the highest priority interrupt is serviced first. In the

example shown in Figure 4-4, if an interrupt is pending upon exit from the interrupt service routine, the

pending interrupt is serviced before the LDA instruction is executed.

Figure 4-4

. 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, save the H

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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