Spartan 3 FPGA LVCMOS18

[nag.chil]

Sir,

 I need to drive 1.8V from Spartan 3 FPGA. I followed as per spartan 3 constraints file. Even though i got the following warnigs and I received 3.3V.

WARNING:XdmHelpers:376 - Unexpected value of "LVCMOS18" found for attribute DRIVE. Unable to convert this to the expected numeric value.
WARNING:Xst:37 - Detected unknown constraint/property "DRIVE". This constraint/property is not supported by the current software release and will be ignored.

[austin]

n,

In addition to setting the IO standard, you must supply 1.8 volts to the Vcco pins for that bank.

[nag.chil]

To set the Vcco 1.8V, Do i need to supply externally or enter the command in constraint file?

[austin]

Both,

Hardware must be connected to 1.8v for that bank, and constraints must match.

[gnarahar]

@nag.chil The setting in the constraint is to let the FPGA fabric know what the expected voltage and IO Standard is so that it can use the respective Voltage thresholds for Inputs and be able to drive with the respective drive strength in case of Outputs. 

As Austin mentioned, both the Hardware and your constraint should be in sync. 

[nag.chil]

Yeah Thank you guys ...

I understood what it is....

So now can u say, in hardware side how can i connect my spartran-3 FPGA bank to 1.8V .......

Any document on that....??

[gnarahar]

@nag.chil Connect the VCCO of that Bank to a 1.8V Power Rail on your board.