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# PSoC 4 MCU

Contributor II

## cmos1.8v GPIO input selection

I need some help please, I cannot seem to find a complete answer in any of the documentation, what is the parameters and use case cmos1.8V gpio selection, does is set the gpio level to be ready for a 1.8V logic signal?  Can it be used if the process is running at 3.3 volts?

I have a peripheral that needs to have the lower voltage signaling, and I cannot implement any additional hardware.

Will CMOS 1.8V allow me to see logic 1 at 2V and 0 at .5V?

1 Solution
Moderator

## Re: cmos1.8v GPIO input selection

Hi,

If you see the VIH and VIL parameter in the datasheet,

VIH = 0.7 x VDDD

VIL = 0.3 x VDDD

in normal case where VDDD is 3.3V,VIH and VIL will be 2.31V and 0.99V, respectively. So any voltage greater than 2.31 will be taken as Logic High and any voltage less than 0.99 will be taken as Logic Low. So 0.5 will be taken as 0 in your case but there no guarantee that 2V will be taken as logic high in your device.

The same can be extended to CMOS 1.8V mode too. Here the VIH and VIL are, 1.26V and 0.54V. So any voltage greater than 1.26V  will be taken as Logic High and any voltage less than 0.54V will be taken as Logic Low.So 0.5V will be taken as logic 0  and 2V will be taken as logic high. But there is one condition that VIH should not exceed VDDD+0.2. This should be maintained for device safety in your case.

Best Regards,
Vasanth

3 Replies
Moderator

## Re: cmos1.8v GPIO input selection

Hi,

If you see the VIH and VIL parameter in the datasheet,

VIH = 0.7 x VDDD

VIL = 0.3 x VDDD

in normal case where VDDD is 3.3V,VIH and VIL will be 2.31V and 0.99V, respectively. So any voltage greater than 2.31 will be taken as Logic High and any voltage less than 0.99 will be taken as Logic Low. So 0.5 will be taken as 0 in your case but there no guarantee that 2V will be taken as logic high in your device.

The same can be extended to CMOS 1.8V mode too. Here the VIH and VIL are, 1.26V and 0.54V. So any voltage greater than 1.26V  will be taken as Logic High and any voltage less than 0.54V will be taken as Logic Low.So 0.5V will be taken as logic 0  and 2V will be taken as logic high. But there is one condition that VIH should not exceed VDDD+0.2. This should be maintained for device safety in your case.

Best Regards,
Vasanth

Contributor II

## Re: cmos1.8v GPIO input selection

Thanks for the detailed reply, so this holds even if the device is running on 3.3V?

Moderator