NEC 78K0 Series User Manual page 494

CHAPTER 19 INTERRUPT FUNCTIONS
Cautions 3. When manipulating a flag of the interrupt request flag register, use a 1-bit memory
manipulation instruction (CLR1). When describing in C language, use a bit manipulation
instruction such as "IF0L.0 = 0;" or "_asm("clr1 IF0L, 0");" because the compiled assembler
must be a 1-bit memory manipulation instruction (CLR1).
If a program is described in C language using an 8-bit memory manipulation instruction such
as "IF0L &= 0xfe;" and compiled, it becomes the assembler of three instructions.
mov a, IF0L
and a, #0FEH
mov IF0L, a
In this case, even if the request flag of another bit of the same interrupt request flag register
(IF0L) is set to 1 at the timing between "mov a, IF0L" and "mov IF0L, a", the flag is cleared to
0 at "mov IF0L, a". Therefore, care must be exercised when using an 8-bit memory
manipulation instruction in C language.
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Preliminary User's Manual U17260EJ3V1UD