When applying the Schmitt_Trigger attribute to an I/O in a CoolRunner-II using the following constraint , NGDBuild issues the warning below:
NET "net_name" SCHMITT_TRIGGER;
"WARNING:NgdBuild:487 - Parameter 'SCHMITT_TRIGGER' on 'net_name' has an incorrect value data type."
Why does this error occur?
This message is identified as a reporting error in NGDBuild. You can verify this by continuing to run through the tool flow by running CPLDFit and reviewing the Fitter report. In the Fitter report under the Inputs section, find the I/O Style of the signal of interest. Look for the "S" under that column. The "S" indicates that the Schmitt Trigger was recognized by the tools and will be applied to the device.
Consequently, you can safely ignore this NGDBuild warning on inputs.
A Schmitt Trigger cannot be applied to an output and this is a valid warning message. The attribute will be ignored.