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CHAPTER 5 INTERRUPT/EXCEPTION PROCESSING FUNCTION
5.3.7 In-service priority register (ISPR)
This register holds the priority level of the maskable interrupt currently accepted. When an interrupt request is
accepted, the bit of this register corresponding to the priority level of that interrupt is set to 1 and remains set while
the interrupt is serviced.
When the RETI instruction is executed, the bit corresponding to the interrupt request having the highest priority
is automatically reset to 0 by hardware. However, it is not reset when execution is returned from non-maskable
processing or exception processing.
This register can be only read in 8- or 1-bit units.
Bit Position
Bit Name
Function
7 to 0
ISPR7 to
ISPR0
In-Service Priority Flag
Indicates priority of interrupt currently accepted.
0: Interrupt request with priority n not accepted
1: Interrupt request with priority n accepted
Remark
n: 0 to 7 (priority level)
5.3.8 Maskable interrupt status flag
The interrupt disable status flag (ID) of the PSW controls the enabling and disabling of maskable interrupt requests.
As a status flag, it also displays the current maskable interrupt acceptance condition.
Bit Position
Bit Name
Function
5
ID
Interrupt Disable
Indicates enabling/disabling of maskable interrupt processing.
0: Maskable interrupt accepting enabled
1: Maskable interrupt accepting disabled (pending)
It is set to 1 by the DI instruction and reset to 0 by the EI instruction. Its value is also
modified by the RETI instruction or LDSR instruction when referencing the PSW.
Non-maskable interrupt and exceptions are acknowledged regardless of this flag.
When a maskable interrupt is accepted, ID flag is automatically set to 1 by hardware.
Interrupt requests generated while interrupts are disabled (ID = 1) are acknowledged
when xxIFn bit of the xxICn register is set (1) and ID flag is reset (0).
Address
FFFFF166H
7
ISPR7
ISPR
6
ISPR6
5
ISPR5
4
ISPR4
3
ISPR3
2
ISPR2
1
ISPR1
0
ISPR0
After reset
00H
31
0
PSW
After reset
00000020H
7
NP
6
EP
5
ID
4
SAT
3
CY
2
OV
1
S Z
8
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0