R8C/20 Group, R8C/21 Group 2. Central Processing Unit (CPU)
Rev.2.00 Aug 27, 2008 Page 12 of 458
REJ09B0250-0200
2.8.7 Interrupt Enable Flag (I)
The I flag enables a maskable interrupt.
An interrupt is disabled when the I flag is set to 0, and are enabled when the I flag is set to 1. The I flag is set to
0 when an interrupt request is acknowledged.
2.8.8 Stack Pointer Select Flag (U)
ISP is selected when the U flag is set to 0; USP is selected when the U flag is set to 1.
The U flag is set to 0 when a hardware interrupt request is acknowledged or the INT instruction of software
interrupt numbers. 0 to 31 is executed.
2.8.9 Processor Interrupt Priority Level (IPL)
IPL, 3 bits wide, assigns processor interrupt priority levels from level 0 to level 7.
If a requested interrupt has greater priority than IPL, the interrupt is enabled.
2.8.10 Reserved Bit
If necessary, set to 0. When read, the content is undefined.
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