HD64F38602R Datasheet, PDF (92/552 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer

Section 3 Exception Handling
3.8.3 Method for Clearing Interrupt Request Flags
Use the recommended method given below when clearing the flags in interrupt request registers
(IRR1 and IRR2).
• Recommended method
Use a single instruction to clear flags. The bit manipulation instruction and byte-size data
transfer instruction can be used. Two examples of program code for clearing IRRI1 (bit 1 in
IRR1) are given below.
Example 1:
BCLR #1, @IRR1:8
Example 2:
MOV.B R1L, @IRR1:8 (set the value of R1L to B'11111101)
• Example of a malfunction
When flags are cleared with multiple instructions, other flags might be cleared during
execution of the instructions, even though they are currently set, and this will cause a
malfunction.
Here is an example in which IRRI0 is cleared and disabled in the process of clearing IRRI1
(bit 1 in IRR1).
MOV.B @IRR1:8,R1L ......... IRRI0 = 0 at this time
AND.B #B'11111101,R1L ..... Here, IRRI0 = 1
MOV.B R1L,@IRR1:8 ......... IRRI0 is cleared to 0
In the above example, it is assumed that an IRQ0 interrupt is generated while the AND.B
instruction is executing.
The IRQ0 interrupt is disabled because, although the original objective is clearing IRRI1,
IRRI0 is also cleared.
3.8.4 Conflict between Interrupt Generation and Disabling
When an interrupt enable bit is cleared to 0 to disable interrupts, the disabling becomes effective
after execution of the instruction. When an interrupt enable bit is cleared to 0 by an instruction
such as BCLR or MOV, and if an interrupt is generated during execution of the instruction, the
interrupt concerned will still be enabled on completion of the instruction, and so interrupt
exception handling for that interrupt will be executed on completion of the instruction. When an
interrupt source flag is cleared to 0, the interrupt concerned will be ignored.
Rev. 3.00 May 15, 2007 Page 60 of 516
REJ09B0152-0300