
R8C/14 Group, R8C/15 Group 20. Precautions
Rev.2.10 Jan 19, 2006 Page 235 of 253
REJ09B0164-0210
20. Precautions
20.1 Stop Mode and Wait Mode
20.1.1 Stop Mode
When entering stop mode, set the FMR01 bit to “0” (CPU rewrite mode disabled) and the CM10 bit to
“1” (stop mode). An instruction queue pre-reads 4 bytes from the instruction which sets the CM10 bit
in the CM1 register to “1” (stop mode) and the program stops. Insert at least 4 NOP instructions after
inserting the JMP.B instruction immediately after the instruction which sets the CM10 bit to “1”.
Use the next program to enter stop mode.
• Program to enter stop mode
BCLR 1,FMR0 ; CPU rewrite mode disabled
BSET 0,PRCR ; Protect disabled
BSET 0,CM1 ; Stop mode
JMP.B LABEL_001
LABEL_001 :
NOP
NOP
NOP
NOP
20.1.2 Wait Mode
When entering wait mode, set the FMR01 bit to “0” (CPU rewrite mode disabled) and execute the
WAIT instruction. An instruction queue pre-reads 4 bytes from the WAIT instruction and the program
stops. Insert at least 4 NOP instructions after the WAIT instruction.
Also, the value in the specific internal RAM area may be rewritten when exiting wait mode if writing to
the internal RAM area before executing the WAIT instruction and entering wait mode. The area for a
maximum of 3 bytes is rewritten from the following address of the internal RAM in which the writing is
performed before the WAIT instruction. The rewritten value is the same value as the one which was
written before the WAIT instruction. If this causes a problem, avoid by inserting the JMP.B instruction
between the writing instruction to the internal RAM area and WAIT instruction as shown in the
following program example.
• Example to execute the WAIT instruction
Program Example MOV.B #055h,0601h ; Write to internal RAM area
...
JMP.B LABEL_001
LABEL _001 :
FSET I ; Enable interrupt
BCLR 1,FMR0 ; CPU rewrite mode disabled
WAIT ; Wait mode
NOP
NOP
NOP
NOP
When accessing any area other than the internal RAM area between the writing instruction to the
internal RAM area and execution of the WAIT instruction, this situation will not occur.
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