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CHAPTER 17 STANDBY FUNCTION
User
’
s Manual U15017EJ2V0UD
17.5 IDLE Mode
17.5.1 IDLE mode setting and operating states
The IDLE mode is selected by setting (to 1) both the STP bit and the HLT bit of the standby control register (STBC).
The only writes that can be performed on STBC are 8-bit data writes by means of a dedicated instruction. IDLE
mode setting is therefore performed by means of the
”
MOV STBC, #byte
”
instruction.
If interrupts are enabled (when the IE bit of the program status word (PSW) is set to 1), write a NOP instruction
three times after the instruction that sets the IDLE mode (after releasing the IDLE mode). Otherwise, two or more
instructions may be executed before an interrupt is acknowledged. As a result, the execution sequence of the interrupt
processing and instructions may be changed. To prevent troubles due to changes in the execution sequence, the
above processing is necessary.
Caution If the IDLE mode is set when the condition to release the HALT mode is satisfied (refer to 17.3.2
HALT mode release), the IDLE mode is not set, but the next instruction is executed or execution
branches to a vectored interrupt service program. To accurately set the IDLE mode, clear the
interrupt request before setting the IDLE mode.
Table 17-6. Operating States in IDLE Mode
Clock oscillator
Oscillation continues
Internal system clock
Stopped
CPU
Operation stopped
I/O lines
Retain state prior to IDLE mode setting
16-bit timer/event counter
Operation stopped
8-bit PWM timer
Operable only when an external input clock
(TIO50, TIO51) is selected as the count clock
Watchdog timer
Stopped (timer is initialized)
A/D converter
Operation stopped
Note 1
3-wire serial interface
Operation stopped
Note 2
Asynchronous serial interface
Operation stopped
Note 2
Watch timer
Operable
External interrupt (INTP0 to INTP2)
Operable
Internal RAM
Retained
Notes 1.
A/D converter operation is stopped, but if the ADCS bit of the A/D converter mode register
(ADM) is set, the current consumption does not decrease.
2.
The serial input pin supports a 3 V interface (i.e., it is a low-threshold pin). To prevent current
being input to the Schmitt input buffer in STOP and IDLE modes, therefore, the Schmitt input
buffer is turned off (the buffer output is
“
L
”
). Disable the serial interface (SIO0, SIO1, SIO2,
and UART) before setting STOP or IDLE mode, and re-set the interface after STOP or IDLE
mode has been released.
Caution The ADCS bit of the A/D converter mode register (ADM) should be reset.