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M16C/64C Group
2.8.7
Interrupt Enable Flag (I Flag)
The I flag enables maskable interrupts.
Maskable interrupts are disabled when the I flag is 0, and enabled when it is 1. The I flag becomes 0
when an interrupt request is accepted.
2.8.8
Stack Pointer Select Flag (U Flag)
ISP is selected when the U flag is 0. USP is selected when the U flag is 1.
The U flag becomes 0 when a hardware interrupt request is accepted, or the INT instruction of software
interrupt number 0 to 31 is executed.
2.8.9
Processor Interrupt Priority Level (IPL)
IPL is 3 bits wide and assigns processor interrupt priority levels from 0 to 7.
If a requested interrupt has higher priority than IPL, the interrupt request is enabled.
2.8.10
Reserved Areas
Only set these bits to 0. The read value is undefined.
R01UH0092EJ0110 Rev.1.10
Jul 31, 2012
2. Central Processing Unit (CPU)
Page 16 of 807
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