R8C/1A Group, R8C/1B Group
2. Central Processing Unit (CPU)
Rev.1.30
Dec 08, 2006
Page 17 of 315
REJ09B0252-0130
2.8.7
Interrupt Enable Flag (I)
The I flag enables maskable interrupts.
Interrupts are 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 is 3 bits wide, assigns processor interrupt priority levels from level 0 to level 7.
If a requested interrupt has higher priority than IPL, the interrupt is enabled.
2.8.10
Reserved Bit
If necessary, set to 0. When read, the content is undefined.