Nec PD750008 User Manual download pdf (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

1 2 ... 211 212 213 214 215 216 217 218 219 220 221 ... 341 342

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