UPD75518 NEC, UPD75518 Datasheet - Page 136

• Manufacturer Part Number: UPD75518
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

136
(2) Multiple interrupt processing by changing the interrupt status flags
As shown in Table 5-3, 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.
Interrupt is disabled.
Low- or high-order
interrupt occurrence
Interrupt is enabled.
Fig. 5-7 Multiple Interrupt Processing by Changing the Interrupt Status Flags
IPS setting
Normal processing
(status 0)
Low- or high-order
interrupt occurrence
Modification
of IST
Interrupt is
disabled.
Interrupt is
enabled.
Single interrupt
Status 1
Status 0
Status 0
Multiple interrupts
Status 1
PD75518(A)