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CHAPTER 17 INTERRUPT/EXCEPTION PROCESSING FUNCTION
User’s Manual U16896EJ2V0UD
550
17.3.6 In-service priority register (ISPR)
This register holds the priority level of the maskable interrupt currently being acknowledged. When the interrupt
request signal is acknowledged, the bit of this register corresponding to the priority level of that interrupt request signal
is set (1) and remains set while the interrupt is being serviced.
When the RETI instruction is executed, the bit among those that are set (1) in the ISPR register that corresponds to
the interrupt request signal having the highest priority is automatically cleared (0) by hardware. However, it is not
cleared (0) when execution is returned from non-maskable interrupt servicing or exception processing.
This register is read-only in 8-bit or 1-bit units.
Reset sets this register to 00H.
Caution If an interrupt is acknowledged while the ISPR register is being read in the interrupt enabled (EI)
status, the value of the ISPR register after the bits of the register have been set to 1 by
acknowledging the interrupt may be read. To accurately read the value of the ISPR register
before an interrupt is acknowledged, read the register while interrupts are disabled (DI status).
ISPR7
Interrupt request with priority n is not acknowledged
Interrupt request with priority n is being acknowledged
ISPRn
0
1
Priority of interrupt currently being acknowledged
ISPR
ISPR6
ISPR5
ISPR4
ISPR3
ISPR2
ISPR1
ISPR0
After reset: 00H R Address: FFFFF1FAH
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Remark
n = 0 to 7 (priority level)