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M16C/6N Group (M16C/6NK, M16C/6NM)
10.5.1 I Flag
The I flag enables or disables the maskable interrupt. Setting the I flag to "1" (enabled) enables the
maskable interrupt. Setting the I flag to "0" (disabled) disables all maskable interrupts.
10.5.2 IR Bit
The IR bit is set to "1" (interrupt requested) when an interrupt request is generated. Then, when the
interrupt request is accepted and the CPU branches to the corresponding interrupt vector, the IR bit is set
to "0" (interrupt not requested).
The IR bit can be set to "0" in a program. Note that do not write "1" to this bit.
10.5.3 ILVL2 to ILVL0 Bits and IPL
Interrupt priority levels can be set using the ILVL2 to ILVL0 bits.
Table 10.3 shows the settings of interrupt priority levels and Table 10.4 shows the interrupt priority levels
enabled by the IPL.
The following are conditions under which an interrupt is accepted:
· I flag = 1
· IR bit = 1
· interrupt priority level > IPL
The I flag, IR bit, ILVL2 to ILVL0 bits and IPL are independent of each other. In no case do they affect one
another.
Table 10.3 Settings of Interrupt Priority Levels
ILVL2 to ILVL0 Bits Interrupt Priority Level Priority Order
000b
Level 0 (Interrupt disabled)
001b
Level 1
010b
Level 2
011b
Level 3
100b
Level 4
101b
Level 5
110b
Level 6
111b
Level 7
Rev.2.00
Nov 28, 2005
REJ09B0124-0200
-
Low
High
page 88 of 378
Table 10.4 Interrupt Priority Levels Enabled by IPL
IPL
Enabled Interrupt Priority Levels
000b
Interrupt levels 1 and above are enabled
001b
Interrupt levels 2 and above are enabled
010b
Interrupt levels 3 and above are enabled
011b
Interrupt levels 5 and above are enabled
100b
Interrupt levels 5 and above are enabled
101b
Interrupt levels 6 and above are enabled
110b
Interrupt levels 7 and above are enabled
111b
All maskable interrupts are disabled
10. Interrupt
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