Datasheet

78K0/Ix2 CHAPTER 18 INTERRUPT FUNCTIONS
R01UH0010EJ0500 Rev.5.00 597
Feb 28, 2012
Figure 18-17. Examples of Multiple Interrupt Servicing (1/2)
Example 1. Multiple interrupt servicing occurs twice
Main processing INTxx servicing INTyy servicing INTzz servicing
EI
EI
EI
RETI RETI
RETI
INTxx
(PR = 1)
INTyy
(PR = 0)
INTzz
(PR = 0)
IE = 0 IE = 0 IE = 0
IE = 1 IE = 1
IE = 1
During servicing of interrupt INTxx, two interrupt requests, INTyy and INTzz, are acknowledged, and multiple interrupt
servicing takes place. Before each interrupt request is acknowledged, the EI instruction must always be issued to enable
interrupt request acknowledgment.
Example 2. Multiple interrupt servicing does not occur due to priority control
Main processing INTxx servicing INTyy servicing
INTxx
(PR = 0)
INTyy
(PR = 1)
EI
RETI
IE = 0
IE = 0
EI
1 instruction execution
RETI
IE = 1
IE = 1
Interrupt request INTyy issued during servicing of interrupt INTxx is not acknowledged because its priority is lower than
that of INTxx, and multiple interrupt servicing does not take place. The INTyy interrupt request is held pending, and is
acknowledged following execution of one main processing instruction.
PR = 0: Higher priority level
PR = 1: Lower priority level
IE = 0: Interrupt request acknowledgment disabled