I am using external interrupt 0 of the 8051 MCU which is connected to to switch. Do I have to use a pull-up resistor? Also, do I have to set the pin as input?

 

It is best to start a new thread on a new topic.

 

What processor?

 

Another quick question. I am using external interrupt 0 which is connected to to switch. Do I have to use a pull-up resistor? Also, do I have to set the pin as input?

Yes, the pin must be configured as input.

A pullup resistor is required. Some microcontrollers have the pullup resistor as an optional feature. Check the datasheet of your MCU.

 

I am using the 8051 MCU.

 

I am using the 8051 MCU.

Download and read the data sheet. It will spell out the requirements on a pin-by-pin basis.