7733 datasheet(96/940 Pages) RENESAS

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7733 Group User's Manual

4–17

INTERRUPTS

4.8 Return from interrupt routine

When the RTI instruction is executed at the end of an interrupt routine, the contents of the program bank

area immediately before the INTACK sequence are automatically pulled. And then, a program returns to the

original routine and the suspended process is resumed.

Before the RTI instruction is executed, by executing the PUL instruction or others, make sure to pull

registers which were pushed by software in an interrupt routine. Make sure that the data length and register

length for the pull operation are equal to those for the push operation.

4.9 Multiple interrupts

When a program branches to an interrupt routine, the following occurs:

q Interrupt disable flag (I) = “1” (Interrupts are disabled.)

q Interrupt request bit of accepted interrupt = “0”

q Processor interrupt priority level (IPL) = Interrupt priority level of accepted interrupt

Therefore, as long as the IPL remains unchanged, by clearing the interrupt disable flag (I) to “0” in an

interrupt routine, an interrupt request whose priority level is higher than the priority level of the interrupt

which is in progress can be accepted. In this way, multiple interrupts are processed.

Figure 4.9.1 shows how multiple interrupts are processed.

An interrupt request which is not accepted because its priority level is lower is held. When the RTI instruction

is executed, the interrupt priority level of the routine which was in progress at acceptance of an interrupt

request is pulled to the IPL. Therefore, if the following relationship is satisfied when interrupt priority level

detection is performed next, the held interrupt request is accepted.

Held interrupt request’s priority level > Processor interrupt priority level (IPL) which is pulled

4.8 Return from interrupt routine, 4.9 Multiple interrupts

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