19.4.2
Multiple Interrupts
When handling multiple interrupts, interrupt handling should include the following procedures:
1. Branch to a specific interrupt handler corresponding to a code set in the INTEVT register. The
code in INTEVT can be used as a branch-offset for branching to the specific handler.
2. Clear the interrupt source in the corresponding interrupt handler.
3. Save SPC and SSR to the stack.
4. Clear the BL bit in SR, and set the accepted interrupt level in the interrupt mask bits in SR.
5. Handle the interrupt.
6. Set the BL bit in SR to 1.
7. Restore SSR and SPC from memory.
8. Execute the RTE instruction.
When these procedures are followed in order, an interrupt of higher priority than the one being
handled can be accepted after clearing BL in step 4. This enables the interrupt response time to be
shortened for urgent processing.
19.4.3 Interrupt Masking with MAI Bit
By setting the MAI bit to 1 in the ICR register, it is possible to mask interrupts while the NMI pin
is low, irrespective of the BL and IMASK bits in the SR register.
•
In normal operation and sleep mode
All interrupts are masked while the NMI pin is low. However, an NMI interrupt only is
generated by a transition at the NMI pin.
•
In standby mode
All interrupts are masked while the NMI pin is low, and an NMI interrupt is not generated by a
transition at the NMI pin. Therefore, standby cannot be cleared by an NMI interrupt while the
MAI bit is set to 1.
Rev. 6.0, 07/02, page 770 of 986
RENESAS [ RENESAS TECHNOLOGY CORP ]
