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(4286) When leaving unused pins open, how should the output latches be set?

Latest Updated:01/16/2006

Question:

(Pin, I/O Port)   When leaving unused pins open, how should the output latches be set? [2006/01/16]

Answer:

The output latch may be set to either 0 or 1 when unused pins are left open.
If the output latch is set to 1, use software to set the corresponding bit in the pull-down control register to 0 (pull-down transistor OFF).
If the output latch is set to 0 and the pull- down transistor is off, the voltage level of the pin is undefined, but power supply current does not increase.
However, power supply current may increase during input instruction execution.
Therefore, set the output latch to 1when there is the possibility of an input instruction targeting unused pins; for example, when there is a mixture of input and unused pins in the ports controlled by simultaneously by a single input instruction. Furthermore, although increased current consumption due to increased power supply current is a disadvantage, the level of current will seldom be enough to damage the ports or the MCU. (#105046)
Suitable Products
4286