Tut 8 : Switch and button

For using swith and button, we would like to understand the concept of pull-up and pull-down resistor. A pull up or pull down resistor are used on Input pins to define a state in the case an input does not have anything connected or the connected part is in the define (high impedance) state. Inputs without a defined state have the problem that the input value can be anything (0 or 1), called floating.

It is useful to steer an input pin to a known state if no input is present. This can be done by adding a pullup resistor (resistor to +5V), or a pulldown resistor (resistor to ground) on the input, with 10K being a common value.

Pull-up resistor

 

Pull-down resistor 



 

PBP Program

'Program to use pull-up resistor(press switch 1) to ON LED1 and pull-down resistor(press switch 2) to ON LED2

 

DEFINE OSC 20 ' using 20MHz clock oscillator

@ device hs_osc

sw1 var PORTD.2

sw2 var PORTD.3 

LED1 var PORTB.6  

LED2 var PORTB.7        

loop:

If (sw1=0) Then                   'sw1 is pressed, pull-up resistor

High LED1

Pause 100                       

End If

 

If (sw2=1) Then                  'sw2 is pressed, pull-down resistor             

High LED2 

Pause 100

End If

 

Goto loop

End