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can anyone tell about GPIO(General Purpose Input/Output)

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Full Member level 2
Jun 19, 2007
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general purpose input output

Hi ,

my question is if we have configured our gpio pins in input mode and one of the input pin is kept floation g then what value will be appear on the corresponding data data register bit .


gpio input noise

Depends on the pin type.

Vaguely, it will usually be in high impedance state and read one, but will comsume more current in such a state.

purpose of gpio

It mean if gpio input pin is floating ,corresponding data register loaction would be in high impedance state and we ll read one.

It would great if you ll explain me why it will be in the high impedance state?


gpio input pin impedance high impedance

The I/O pin has both an input and an output connection.

If the output connection is not in high impedance state, it will interfere with the input signal. So if the pin is configured as input-only, the output connection will be in high impedance state.

With the output connection in high impedance state, if the input is unconnected, it can be sensitive to noise sources (for example, RFI and EMI).

general purpose input/output

firstival it is not good practice to have floating pins. Even if pin is not connected it does not garantee what level at the coresponding output you will have.

High immpidance control throught the separate control line of the output buffer.

Please look in to the data spec for your FPGA

gpio uc current sink

my simple question is if i have configured gpio pi as input and that pin is floating then what vale i will read in the data register corresponding to that pin.


input floating mode of gpio

That's real hard to sayUNLESS you say what the uC is.. or show us it's datasheet.

But as I said before, it will be mostly 1.

gpio floating input

Hi vsmGuy,

I am really thankful to for your answer but if you explain me why It will be great and my confusion will be clear.Please elaborate it for more understanding.

Thnaks & Regards

gpio pin as a trigger for fpga

For all CMOS pads, it will be undefined, can be 0 can be 1(but definitely not high impdence, because you have configured this pad as input, i.e you have enabled the transistor producing a high impedence), and may fluctuate between 0 and 1. This is because, the CMOS gate has a capability to pick up charge from air, and this charge is sometimes enough to trigger the gate. So it is really undefined, and it is definitely NOT recommended to keep any pin afloat.
However if the pad is made with TTL logic, then open input always produces an '1' at the TTL gate output. I.e you will latch a logic '1' at your corresponding register. This is because: In order to drive a TTL input to a '0', you must sink current from the transistor into ground. Leaving it open won't sink the current to ground, and so, the input transistor remains OFF, and if you look at TTL circuit, if the input transisotr is OFF, then the output '1'.
Hope it helps,

input pin not connected

now it clear to me...thanks alot avimit

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