GPIO question

[andy257]

Hi All,

I have a single board computer that outputs 3.3V on its GPIO port. The trouble is that a couple of the pins on the GPIO port are actually 5V and GND. My understanding was that the I/O would then be 5V/GNd logic not 3.3V. Does anyone have any ideas why this is?

When i measure from output to ground its 3.3V, but if i measure output to 5V i see 1.7V, why is this?

Thanks

 

[RCinFLA]

Assuming this is a CMOS circuit, you either have a separate 3.3 v supply for I/O or there is excessive load on I/O.

CMOS driver with light output loading will be very close to supply rail.

Are you sure some of these I/O are not programmed as inputs? All inputs need to be driven low or high so they don't float. Holding a CMOS gate in middle of supply range will cause both P-ch and N-ch output MOSFET's to draw current causing excessive current drain.

 

[andy257]

With no load connected to the I/O i measure 3.3V output. There are separate pins for input and separate pins for output so i am assuming they dont need to be configured as input or output.

I just assumed because the the two most right hand pins on the header are 5v / GNd on the GPIO port??

 

[Mikebits]

It might be 3.3v logic with 5v tolerant inputs. It is hard to say without knowing the device you are talking about.

 

[RCinFLA]

Why do you think it should be 5v? Just because board takes a 5v supply?

Most processors today are smaller geometry that can not tolerate 5vdc. I bet the board has a 3.3 v regulator.

90 nanometer parts have dual oxide options. Single oxide core processor runs at 1.3 vdc and I/O (having dual oxide layer gates) can tolerate up to about 3.5 vdc.

Most Intel parts over last year are 45 nm geometry. Core processor runs at 0.9vdc, I/O at 3.3vdc.