[SOLVED] Pull-up Resistor in PORT 0

Hai..

Why we have to connect pull-up resistor in PORT0.? why not in other PORTS??
Can't we make same architecture to PORT0 like other PORTS??

please clarify these doubts..

thanks in advance..

Read in this datasheet Page no. 5 & 6

**broken link removed**


https://www.engineersgarage.com/forums/8051/pull-resistor

I hope its helps you

Beacuse they are either open collector or open drain ports. So pullups are needed. The other ports are not open collector or open drain type.

jayanth.devarayanadurga said:

Beacuse they are either open collector or open drain ports. So pullups are needed. The other ports are not open collector or open drain type.

Click to expand...

hai jayanth,

my question is... why we need this different?? why we want to use open collector or open drain in PORT0.?

Ask the designer of 8051.

You can see an open collector o/p used in IC. In same way we have open drain o/p in 8051 port0. The output essentially acts as either an open circuit (no connection to anything) or a connected to ground. we use external pullup resistor to provide high volt (1) rather than providing open circuit output.



Because the pull up resistor is external and need not be connected to the chip supply voltage, a lower or higher voltage can be used instead. Open collector circuits are therefore sometimes used to interface different families of devices that have different operating logic voltage levels or to control external circuitry that requires a higher voltage

_______________________________________________________________________
this useful post copied from this link
https://www.engineersgarage.com/forums/8051/pull-resistor

Completely agree with #MAAM#

Pull-ups are used so that components with a different driving voltage can be connected to the microcontroller. And as we don't need many of such components together, only one port is made so. If yo need more, you need to use any driver.

jayanth.devarayanadurga said:

Ask the designer of 8051.

Click to expand...

hai jayanth,

i know to ask with 8051 designer, you don't want to say. if you don't know means simply stay out **?

:lol:

sorry if i hurted...

- - - Updated - - -

errakeshpillai said:

Completely agree with #MAAM#

Pull-ups are used so that components with a different driving voltage can be connected to the microcontroller. And as we don't need many of such components together, only one port is made so. If yo need more, you need to use any driver.

Click to expand...

can you say any example??? different driving voltage mean, we can get more then 5V from PORT0 ? is it???

You got it wrong. We cannot get more than 5V from Port 0. Actually it is not the output voltage of Port 0 that we get at its pin (the reason being Open Drain/Collector configuration). The output of Port 0 will just connect the Pull-up resistor supply to the output.

Follow this link to get your doubts clarified. Read the introduction and the applications part carefully.
Wikipedia - Open Collector

I guess, this should clarify your doubts. If any doubts get back.

errakeshpillai said:

You got it wrong. We cannot get more than 5V from Port 0. Actually it is not the output voltage of Port 0 that we get at its pin (the reason being Open Drain/Collector configuration). The output of Port 0 will just connect the Pull-up resistor supply to the output.

Follow this link to get your doubts clarified. Read the introduction and the applications part carefully.
Wikipedia - Open Collector

I guess, this should clarify your doubts. If any doubts get back.

Click to expand...

thank you rakesh...

I Got you...
My doubts are clarified....