Are the inputs to microcontrollers high impedance?

[chris414]

This may be an obvious question but I just want to make sure - if I set a pin on my PIC18F2550 to be an input, does that pin automatically become a high impedance input? Ie. will I be able to connect the pin straight to the positive supply rail without fear of blowing the PIC?

 

[ericgibbs]

This may be an obvious question but I just want to make sure - if I set a pin on my PIC18F2550 to be an input, does that pin automatically become a high impedance input? Ie. will I be able to connect the pin straight to the positive supply rail without fear of blowing the PIC?

hi Chris,
A PIC pin when set as an Input does have an high impedance, but do not connect any voltage greater than the +Vs supply the PIC's power rail, also no negative input voltage.

Do you have a specific question regarding a voltage you want to connect to the PIC.??

 

[chris414]

Thanks for the reply - no, I am only using 5V... I was just wondering whether I needed a "protecting" resistor to limit current to the PIC, but which obviously I dont need now since it's a high impedance input

 

[MikeMl]

You DO need a series resistor if the 5V that the input is connected to can be there when the PIC's VDD pin is not yet powered.

 

[crutschow]

It's always good practice to use a limiting resistor is case the pin is accidentally set as an Output at any time.

 

[blueroomelectronics]

Why would you want to connect an I/O pin to power? What would be the purpose?
Unused I/O pins should be set to outputs.