GPIO input voltage level

[masahirokiniwa]

I'm considering to use the GPIO of LPC802 as a comparator.
Can I input continuous midpoint potential to it?

In the data sheet, LPC802 supports 0V to 3.6V.
But I couldn't see the availability to input it.

Best regards,
M.Kiniwa

[victorjimenez]

Hi M.Kiniwa, 

The answer that Ian Benton gave is correct. You wont have any problem if you supply any voltage (that is within the allowed values) continuously. 

Hope it helps! 

Victor.

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[victorjimenez]

Hello M.Kiniwa,

Do you want to know the input voltage supported? If so, please refer the data sheet of the LPC802 (Data sheet.pdf) In chapter 10 table 9 you will fin the limiting values.

Hope it helps! 

Victor.

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[masahirokiniwa]

Hi Victor,

Thank you for your reply.

I care when I continue to input midpoint like 1.5V, can LPC operate correctly and doesn't get damage?

I think that midpoint potential is in limiting values, so LPC can operate correctly. But normally GPIOs are input continuously high or low level.

I'd like to confirm that LPC allow my usage as above.

Best regards,

M.Kiniwa

[ianbenton · Accepted solution]

Yes, it won't do any harm. Is just a standard CMOS input, like any other 74HC gate.

Two things to watch out for:

1) it will increase the supply current, maybe as much as a milliamp. So don't do this if really low power is important.

2) the processor may read it as a ONE, it may read it as a ZERO. ANd how it reads it on your prototype won't predict how it will read it on a production run.

[ianbenton]

You mean using the GPIO itself rather than a comparator?

There would be two problems.

1) Biassing a digital input to a voltage midway between the supplies will make it draw supply current. Could be as much as a mA or two.

2) The guaranteed logic thresholds are 1V and 2V; so at 1.5V it could read your input as a 1 and it could read it as a 0, depending where the threshold on your particular device is. It will function as a comparator, but you never know quite where the threshold will be, other than it will be SOMEWHERE between 1V and 2V.