Note:

In the products other than those concerned, this problem does not occur because BTSTC and BTSTS instructions are not generated if any of the above-mentioned optimizing options is used.

• Suppress the generation of the BTSTC and BTSTS instructions resulting from using an optimizing option by selecting the -ONA (or -Ono_asmopt) option together with any of the above-mentioned optimizing options.
• Add an asm function to disable optimization locally, as shown in the example below.

  Example:
  -----------------------------------------------------------------------
  while(TA0IC.IR==0)
   {
         asm();       /* An asm function added to disable optimization 
                         for TAOIC.IR */
   }
  -----------------------------------------------------------------------

-------------------------------------------------------------------------
#pragma ADDRESS TA0IC   0055h   /* M16C/62 MCU's Timer A0 interrupt 
                                                   control register */

struct {
    char    ILVL : 3;
    char    IR   : 1;           /* An interrupt request bit */       
    char    dmy  : 4;
} TA0IC;

void wait_until_IR_is_ON(void)
{
     while (TA0IC.IR == 0)      /* Waits for TA0IC.IR to become 1 */
    {
        ;
    }
    TA0IC.IR = 0;               /* Returns 0 to TA0IC.IR 
                                                 when it becomes 1 */
}
-------------------------------------------------------------------------

[Precautions for Interrupts]
When a instruction to rewrite the interrupt control register is executed but the interrupt is disabled, the interrupt request bit is not set sometimes even if the interrupt request for that register has been generated. This will depend on the instruction. If this creates problems, use the below instructions to change the register.

Instructions: AND, OR, BCLR, BSET

When writing to or reading a register in the SFR area, it may sometimes be necessary to use a specific instruction. Because this specific instruction varies with each type of MCU, consult the user's manual of your MCU for details.
In this case, write the instruction directly in the program using the ASM function.

[Related Documents]

NC308 User's Manual:	3.1.2 Notes about the M16C's Type Dependent Part
NC30 User's Manual:	3.1.2 Notes about the M16C's Type Dependent Part
M3T-NC308WA Release Note:	Precaution M16C Family-Dependent Code
M3T-NC30WA Release Note:	Precaution M16C Family-Dependent Code

Note: Although the above descriptions are not found in several documents released before 2000, the same cautions should be observed in those cases.