Skip to main content
Knowledgebase
Home
Renesas Electronics Europe - Knowledgebase

What happens when unused pins are left open?

Latest Updated:09/11/2012

Question:

What happens when unused pins are left open?

Answer:

Unused pins are configured as follows typically:

- Input-dedicated pin: Fixed (pull-up, pull-down, connected to the power supply or ground)
- Output-dedicated pin: Open
- I/O pin: Fixed to input (pull-up or pull-down), or left open to output
- NC pin: Connection is not allowed

When the input pin does not install a resistor to connect with the power supply directly or ground, the pin may be affected by the spike noise on the power supply line, and may cause malfunction.
Or, when an unexpected accident occurs to damage the CPU input protection circuit, a large current flows through the CPU which may damage the CPU terminally. So, we recommend installing a pull-up resistor or pull-down resistor with the unused input pin (or I/O pin which is set to input).

Install the pull-up or pull-down resistors between 4.7 kΩ to 100 kΩ.
As the pins with weak keeper has limitations on the resistor value, refer to the manual of the MCU. Configuration of some are specified by Renesas. Make sure to refer the Hardware Manual of the MCU.

When leaving the input-dedicated pin or I/O pins (default: input port) open, it is possible that the pin floats to the midpoint voltage would cause the through current in the MCU internally. A through current may degrade or damage the pins.

 

Suitable Products
SH7285, SH7286
SH7265
SH7263
SH7262, SH7264
SH7243
SH7214, SH7216
SH7231
SH7239, SH7237
SH7211
SH7206
SH7205
SH7203
SH7124, SH7125
SH7670
SH7619
SH7146, SH7149
SH7144, SH7145
SH7131, SH7132, SH7136, SH7137
SH7083, SH7084, SH7085, SH7086
SH7065
SH7058
SH7055
SH7052, SH7053, SH7054
SH7047, SH7049, SH7105, SH7107, SH7109
SH7046, SH7148, SH7101, SH7048, SH7104, SH7106, SH7108
SH7040, SH7041, SH7042, SH7043, SH7044, SH7045
SH7032, SH7034, SH7034B
SH7020, SH7021
SH7018
SH7014, SH7016, SH7017
SH7011