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CHAPTER 24
STANDBY FUNCTION
User’s Manual U12697EJ4V1UD
24.6 Check Items When Using STOP or IDLE Mode
The following points must be checked to decrease the current consumption when using the STOP mode or IDLE
mode.
(1) Is the output level of each output pin appropriate?
The appropriate output level of each pin differs depending on the circuit in the next stage. Select the output level
so that the current consumption 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 current consumption 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 current consumption 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 current consumption sometimes increases when a low level
is input. In this case, output a high level or high impedance to reduce the current consumption.
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 current consumption 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 use pull-up or pull-down
resistors.
The setting method for the output level differs depending on 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 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 software
when in the port mode.
When the port enters the control mode, the port mode is changed by simply setting the output level.
(2) Is the input level to each input pin appropriate?
Set the voltage level input to each pin within a range from the VSS voltage to the VDD voltage. If a voltage outside
of this range is applied, not only does the current consumption increase, but the reliability of the
PD784225 is
negatively affected.
In addition, do not increase the middle voltage.
(3) Are internal pull-up resistors needed?
Unnecessary pull-up resistors increase the current consumption and are another cause of device latch-up. Set
the pull-up resistors to the mode in which they are used only for the required parts.
When the parts needing pull-up resistors and the parts not needing them are mixed together, externally connect
the pull-up resistors where they are needed and set the mode in which the internal pull-up resistors are not used.