Solution:
In order to assign a 3.3V inputs to a 1.5 V bank on the top side of a LatticeECP3 device (Bank 0 and Bank1), turn off the PCICLAMP in
Spreadsheet view for the respective bank. By default, the PCICLAMP is ON for all the banks and hence,
Lattice Diamond Software will give an error while mixing 3.3V inputs to a 1.5V bank.