Handling of Unused Pins

How should I handle unused pins?

1. Input pins
   These pins cannot be left open.
   Connect input pins to the power supply or ground.
   (except when these pins are pulled up or down internally)
   
   
2. Output pins
   These pins can be open.
   However, we recommend connecting open-drain output pins to the same electric potential line (power supply or ground) as potential of the pins whose transistor is in the ON to protect against damage due to static electricity.
   
   
3. I/O pins (data bus, address bus, I/O ports, etc.)
   The handling differs depending on the function.
   Set the pins in the output mode whenever possible.
   In this case, these pins can be handled in the same way as output pins.
   If the pins may become input pins, pull them up (or down) using an appropriate resistor for each.
   

The pin processing procedures of some of the RF/microwave devices differ from one another. For details, consult your nearest distributor. Regarding photocouplers having many channels, however, all the pins of the unused channel should be grounded to make their potential the same, or left open.

(2008/02)

Is the NC pin a pin to which nothing can be connected?
I do not understand the difference between this pin and an IC pin.

An NC (Non-Connection) pin is a pin that is not internally connected.
However, when a signal wire, etc., is connected to the pin, this might cause a worsening of the internal noise environment, and therefore it is recommended to be open.

By contrast, an IC (Internally Connected) pin is connected internally, so the state of the pin may define the internal operation.
Handle the pin as directed.

Consult a sales representative or a distributor, because the processing method of the RF & microwave devices differs depending on the product.

(2007/04)

It is recommended that the pins during input be pulled up to the power supply or pulled down to the ground with resistors and the pins during output be open as processing of unused pins for the I/O ports of microcontrollers, but is either fine?
Why are the resistors needed?

Either input and output is fine. However, I/O ports become input ports after reset, so that pulling them up/down with a resistor is the best processing method.
If a reduction in the number of parts is absolutely desirable, it is recommended to set the ports to output. In this case, a through current may flow until output is set, but since this is caused by voltage fluctuated by noise and not by voltage fixed at a midpoint voltage, this current does not flow continuously. If output is set immediately after reset, no problems, such as damage, will occur.
Even if a pin is left set to input, taking into consideration the possibility that the pin may change to output as the result of program hangup or noise, the insertion of a resistor is recommended. Only dedicated input ports, since they can be changed to output, can be connected directly to the power supply or ground.
However, in the case of systems that must maintain high reliability over many years, the insertion of resistors is preferable even for dedicated input ports. While this is extremely rare, if a current flows to the gate input due to product degradation, the current of the entire system may be pulled, resulting in system down.

(2007/11)

It is recommended to leave open output-only general-purpose ports when they are not used. Is it all right to connect them to the power supply by setting their output level to high or to the ground by setting their output level to low?
If there is any problem, can it be avoided by inserting a resistor?

Although there is no problem in the ordinary status, there is a rare possibility of the output level being reversed by the influences of noise on the signals, power, and ground. This may create a short-circuiting status and expedite degradation of the product even though the product is not instantaneously damaged.
The short-circuiting can be avoided if a pull-up or pull-down resistor is connected, but with current flowing. If this current does not exceed absolute maximum ratings and recommended operating conditions, then there is no particular problem with connecting them as inquired.

(2008/02)

I'm using an analog switch at the input of the uPC339, so a high-impedance state exists at the switch timing, which means that the input pin is briefly open at this timing.
Is this OK?

This will not damage the device.
Note, however, that the output pin may become high level if it is open.

I imagine that the switch time in your case is short, so there shouldn't be a problem.
However, whether this brief open state will affect the operation of the device or not depends on the usage conditions.

Therefore, check the effect of this open state under your actual usage conditions.

When handling unused pins, is it prohibited to bundle pins described as "via individual resistors" and pull them all up or down with a single resistor?

Yes, this is prohibited.
Pins that are thus described are I/O pins that include outputs that are not open collector or open drain.
Output conflicts may occur for this reason, so wired OR connection is not possible.