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CHAPTER 25 STAND-BY FUNCTION
25.6 Chack Items When Using STOP or IDLE Mode
The checks required to decrease the consumption current when using the STOP mode or IDLE mode are described
below.
(1) Is the output level of each output pin appropriate
The appropriate output level of each pin differs with the circuit in the next stage. Select the output level so that
the consumption current is minimized.
If a high level is output when the input impedance of the circuit in the next stage is low, current flows from
the power source to the port, and the consumption current increases. This occurs when the circuit in the next
stage is, for example, a CMOS IC. When the power supply is turned off, the input impedance of a CMOS
IC becomes low. To suppress the consumption current and not negatively affect the reliability of the CMOS
IC, output a low level. If a high level is output, latch-up results when the power supply is applied again.
Depending on the circuit in the next stage, the consumption current sometimes increases when a low level
is input. In this case, output a high level or high impedance to eliminate the consumption current.
When the circuit in the next stage is a CMOS IC, if the output is high impedance when power is supplied to
the CMOS IC, the consumption current of the CMOS IC sometimes increases (in this case, the CMOS IC
overheats and is sometimes destroyed). In this case, output a suitable level or pullup or pulldown resistors.
The setting method for the output level differs with the port mode.
Since the output level is determined by the state of the internal hardware when the port is in the control mode,
the output level must be set while considering the state of the internal hardware.
The output level can be set by writing to the output latch of the port and the port mode register by the software
when in the port mode.
When the port enters the control mode, the port mode is changed by simply setting the output level.