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why we need to connect pull up resistor to port 0 and what haappen if we dont ?? tell me some intresting abt it i know the basics of port0 ….. i had checked for both the conditions
and is pull up is essencial for connecting loads to port 0 or for all connections???
The 8051 microcontroller does not has internal pull up for port 0, for rest of the ports it has internal pull up so u dont need to connect.
i already knew it dude ,,,,,,, i am seeking for some extraorinary information that i never had heard ……. what is the funda of pull up?
The key function for the resistor itself is to prevent too much current from flowing through the pins..
and if we dont connect it ..noting will happen…:
hi ..
what happened if the transistor is ON . vdd has a direct connection to ground as shown in equivalent switch diagram .it will short out the circuit. high current will flow.high current increase the temprature. if you are not lucky port pin might be burn out..
so u have to connet a resitor at drain called pull up resistor . it limits the current.it also provide correct logic levels when the transistor is on or off..
when the transistor is off it pulls up the drain terminal at high logic level thats what required…
that was really nice but now question arises is that pull up resistor is required only if want to connect some load to port0 pin or its also essential if we want to send high and low logic simply …… for eg, if lcd pins RS, RW and E pin is connected to port0 then pull up is required or not ?????and why pull up is not inbuilt in 8051family if its too essential ????????
yes ..if u r using port0 as i/o pin u must have to connect pull up resistor .
if u are not using pull up resistor it gives logic 0 but will not gives logic 1 , instead it floats (high z) .
2nd question is why it does not have built in pull up resistor.
The P0 port is characterized by two functions.
PO is used to interface external external memory .
If u have to interface external memory then the
address/data is applied on it. Port 0 is also designated as AD0-AD7, allowing it to be used for both address and data..address and data is multiplexed.
Otherwise, all bits of this port are configured as I/O pins.
when extrnal memory is connected to port 0 then microcontroller will provide internal power source to its pins so there is no need to connect external pull up resistor.
wysiwyg_imageupload:3014:height=228,width=525
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
hello dharmik….
you know basic about port 0 so as we know that port 0 has multiplex address and data bus so
if we not connect external pullup than it will sink current from both one from inside supply as well as outer vcc supply and it would be a large current flow through internal transistor so it will damage port so thats why…..we use external pull up resistor is used in port 0 rathar than other port because other port not have any multiplexing add or data bus.
thanks all of you …. what is the internal structure of resistor array how to connect it to port0 if we want ???
and which array is most suitable for atmel 89c51 4.7k or 10k…….?
since all other ports have 10k internal pull up resistor my suggestion is to go for 10k resistor. But the value of the pull up also depends for what you are using the pins for
hello everyone
for past two weeks i am trying to do 4*4 keypad interfacing with 89c51 but i am not getting the output i can see only shuffled values in lcd not the assigned values plz help with the design and programming
i am using keilc compiler and proload for dumping wysiwyg_imageupload:3455:is there any problem with my circuit plzzz help me
or mail me at
sramesh1992@gmail.
com
hi guys,
extension of this doubt…
why is the value of pull-up resistor used = 10k? for a supply of 5V, this yields a current of 0.5mA..
How does the microcontroller know whether there is a high signal or low signal on this pin?
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