How to give a +5V or 0V as a input to 89C2051?

[dtparekh]

Re: inputs to 89C2051???

Hello friends!

Can u tell me how to give a +5V or 0V as a input to 89C2051?
i want information on internal pull up facility i am not getting what is meant by pull up?

Thanks

Added after 1 hours 48 minutes:

input is meant as to the port pins of port1 & port-3

 

[FoxyRick]

Re: inputs to 89C2051???

Pull-up resistors are used because the pin drivers are open-drain. That means that they can connect to 0V, but not to +5. Without the pull-ups, when set to output 1, the output will just float. With the pull-up, the pin is connected through the resistor to +5V when output is set to 1.

This is why an LED, for example, is usually connected between the pin and +5V, rather than ground.

To use as inputs, just define them as input (write '1' to them), driving the pin high through the pull-up. You can then give the pin 0 or +5V and read its value. When giving it 0, the pin will source current through the pull-up resistor. Your driving circuit must have a lower impedance than the pull-up resistor, or it might not pull down to 0 enough (it makes a potential divider with the pull-up). Note also that no connection to a pin will read as a '1' due to the pull-up.

FoxyRick.

 

[Davood Amerion]

inputs to 89C2051???

use one transistor (eg. C1815) as follow:
emitter to ground
base to Resistor (eg. 22K)
collector to one of 89X51 port pin.
connect input voltage 0-5 volt to other side of above resistor.
and in program initialization write 1 to that pin to configure it as input.