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CHAPTER 22
INTERRUPT FUNCTIONS
User’s Manual U12697EJ4V1UD
22.7.3 Maskable interrupt priority levels
The
PD784225 performs multiple interrupt servicing in which an interrupt is acknowledged during servicing of
another interrupt. Multiple interrupts can be controlled by priority levels.
There are two kinds of priority control, control by default priority and programmable priority control in accordance
with the setting of the priority specification flag. In priority control by means of default priority, interrupt servicing is
performed in accordance with the priority preassigned to each interrupt request (default priority) (refer to Table 22-
2). In programmable priority control, interrupt requests are divided into four levels according to the setting of the priority
specification flag. Interrupt requests for which multiple interruption is permitted are shown in Table 22-5.
Since the IE flag is cleared (0) automatically when an interrupt is acknowledged, when multiple interruption is used,
the IE flag should be set (1) to enable interrupts by executing the IE instruction in the interrupt service program, etc.
Table 22-5. Multiple Interrupt Servicing
Priority of Interrupt Currently
ISPR Value
IE Flag in PSW
PRSL in
Acknowledgeable Maskable Interrupts
Being Acknowledged
IMC Register
No interrupt being
00000000
0
×
 All macro service requests only
acknowledged
1
×
 All maskable interrupts
3
00001000
0
×
 All macro service requests only
10
 All maskable interrupts
11
 All macro service requests
 Maskable interrupts specified as
priority 0/1/2
2
0000
×100
0
×
 All macro service requests only
1
×
 All macro service requests
 Maskable interrupts specified as
priority 0/1
1
0000
××10
0
×
 All macro service requests only
1
×
 All macro service requests
 Maskable interrupts specified as
priority 0
0
0000
×××1
××
 All macro service requests only
Non-maskable interrupts
1000
××××
×
 All macro service requests only
0100
××××
1100
××××