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Rev.1.02 Jul 01, 2005 page 63 of 314
REJ09B0126-0102
M16C/6N Group (M16C/6NL, M16C/6NN) 9. Interrupt
Under development
This document is under development and its contents are subject to change.
9.5.1 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.
9.5.2 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.
9.5.3 ILVL2 to ILVL0 Bits and IPL
Interrupt priority levels can be set using the ILVL2 to ILVL0 bits.
Table 9.3 shows the settings of interrupt priority levels and Table 9.4 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 9.4 Interrupt Priority Levels Enabled by IPL
Table 9.3 Settings of Interrupt Priority Levels
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
ILVL2 to ILVL0 Bits
Interrupt Priority Level
Priority Order
000b Level 0
(Interrupt disabled)
-
001b Level 1 Low
010b Level 2
011b Level 3
100b Level 4
101b Level 5
110b Level 6
111b Level 7 High