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CHAPTER 2 HANDLING DEVICES
2.1
Precautions on Handling Devices
This section describes the precautions to be taken when handling the power supply
voltage, pins, and other device items.
s Precautions on Handling Devices
r Ensure that the voltage does not exceed the maximum ratings. (Preventing latchup)
A latchup may occur if a voltage higher than Vcc or lower than Vss is applied to input or output
pins other than middle- or high-level resistant pins, or if voltage exceeding the rated value is
applied between Vcc and Vss.
When a latchup occurs, the supply current increases rapidly, occasionally resulting in
overheating. Therefore, ensure that the voltage does not exceed the maximum ratings when
using the microcontrollers.
Also, when turning the analog system power supply on or off, ensure that the analog input does
not exceed the digital power supply (Vcc).
r Stabilize the supply voltage as much as possible
Although the specified Vcc supply voltage operating range is assured, a sudden change in the
supply voltage within the specified range may result in a malfunction.
The following stabilization guidelines are recommended:
The Vcc ripple (P-P value) at the
supply frequency (50 to 60 Hz) should be less than 10% of the typical Vcc value, and the
coefficient of excessive variation should be less than 0.1 V/ms instantaneous change when
switching the power supply.
r Handling unused input pins
Leaving unused input pins open may result in a malfunction or equipment damage due to a
latchup. Therefore, set these pins to pull-up or pull-down via resistors 2 k
or higher.
For unused input pins, open the pins in the output state.
Alternatively, perform the same
processing as for input pins in the input state.
r Handling the N.C. pins
Ensure that the N.C. (internally connected) pins are open before using.
r Handling the power supply pins of a model with an A/D converter
Even if the A/D converter is not used, connect so that AVss = Vss.
r Precautions on using an external clock
When an external clock is used, the oscillation stabilization time is also provided for power-on
reset and stop mode release.
r Wild register function
Because wild registers cannot be debugged on MB89PV930A, check operation on an actual
MB89P935A.