
248
CHAPTER 16 INTERRUPT FUNCTION
User
’
s Manual U15017EJ2V0UD
16.3.3 In-service priority register (ISPR)
The ISPR shows the priority level of the maskable interrupt currently being serviced and the non-maskable interrupt
being serviced. When a maskable interrupt request is acknowledged, the bit corresponding to the priority of that
interrupt request is set to 1, and remains set until the service program ends. When a non-maskable interrupt is
acknowledged, the bit corresponding to the priority of that non-maskable interrupt is set to 1, and remains set until
the service program ends.
When an RETI instruction or RETCS instruction is executed, the bit, among those set to 1 in the ISPR, that
corresponds to the highest-priority interrupt request is automatically cleared to 0 by hardware.
The contents of the ISPR are not changed by execution of an RETB or RETCSB instruction.
RESET input sets the ISPR to 00H.
Figure 16-3. Format of In-Service Priority Register (ISPR)
Caution The in-service priority register (ISPR) is a read-only register. The microcontroller may malfunction
if this register is written.
ISPR
0
7
6
5
4
3
2
1
WDTS
0
0
ISPR3
ISPR2
ISPR1
0
ISPR0
Address: 0FFA8H
Symbol
R
After reset: 00H
WDTS
0
1
Watchdog timer interrupt servicing status
Watchdog timer interrupt (non-maskable interrupt: INTWDT)
is not acknowledged.
Watchdog timer interrupt (non-maskable interrupt: INTWDT)
is acknowledged.
ISPRn
0
1
Priority level (n = 0 to 3)
Interrupt of priority level n is not acknowledged.
Interrupt of priority level n is acknowledged.