NEC PD750008 - Manual (Page 216)

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µPD750008 USER'S MANUAL
6.5 MULTIPLE INTERRUPT PROCESSING CONTROL
The µPD750008 can handle multiple interrupts by either of the following methods.
(1) Multiple interrupt processing by a high-order interrupt
In this method, the µPD750008 selects an interrupt source among multiple interrupt sources, enabling
double interrupt processing.
That is, the high-order interrupt specified by the interrupt priority specification register (IPS) is enabled
when the processing status is 0 or 1. Other interrupts (interrupts lower than the specified high-order
interrupt) are enabled only when the status is 0. (See Figure 6-8 and Table 6-3.)
When only one interrupt is used as a level-two interrupt, using this method saves the user the trouble of
enabling or disabling interrupts during an interrupt processing, and holds down the number of nesting
levels to two.
Figure 6-8. Multiple Interrupt Processing by a High-Order Interrupt
Normal
processing
(Status 0) Low- or high-order
interrupt processing
(Status 1) High-order
interrupt
processing
(Status 2)
Interrupt is disabled.
IPS setting
Interrupt is enabled.
Low- or high-order
interrupt occurrence
High-order
interrupt
occurrence