Error (10779): VHDL error at < filename.vhd >: expression is not constant. - Error (10779): VHDL error at < filename.vhd >: expression is not constant. Description Due to a problem in the Quartus ® II software version 13.1 and earlier, you may see this error message if you use a variable as an index for signal. For example : data(a downto b) where a and b are variables Resolution To workaround this problem, use a 3rd party synthesis tool or avoid this code construct. This problem is scheduled to be fixed in a future release of the Quartus II software. Custom Fields values: ['novalue'] Troubleshooting novalue False ['novalue'] ['FPGA Dev Tools Quartus II Software'] novalue 12.1 ['Programmable Logic Devices'] ['novalue'] ['novalue'] ['novalue']