NEC PD750008 - Manual (Page 217)

197
CHAPTER 6 INTERRUPT AND TEST FUNCTIONS
(2) Multiple interrupt processing by changing the interrupt status flags
Changing the interrupt status flags with the program causes multiple interrupts to be enabled. That is,
when the interrupt processing program changes both IST1 and IST0 to 0 (status 0), multiple interrupt
processing is enabled.
This method is used when two or more interrupts are to be enabled at a time or when the processing of
three or more interrupts is to be performed.
When changing IST1 and IST0, interrupts must be disabled beforehand with a DI instruction.
Figure 6-9. Multiple Interrupt Processing by Changing the Interrupt Status Flags
Low- or high-order
interrupt occurrence
Normal processing
(status 0) Single interrupt Dual interrupts
Interrupt is enabled.
Low- or high-order
interrupt occurrence
Interrupt is
disabled.
Modification
of IST
Interrupt is
enabled.
Status 1
Status 0
Status 0
Status 1
IPS setting
Interrupt is disabled.