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AR# 4376

FPGA Express: How to assign standard logic vectors as Hex or Octal values


Keywords: hex, FPGA, Express, VHDL, std_logic_vector, vector

Urgency: Standard

General Description:
When assigning std_logic_vectors a Hex value within FPGA Express 2.x like so:


the following Error is returned

Error L20/C0 : #0 Error: <file>.vhd line <x> Can not determine type of right
hand side. The following interpretations were considered for the right hand
side: (none). (VSS-1049) (FE-dm-hdlc-unknown)

This problem has been fixed in FPGA Express 3.0, although leaving the
conversion function in will give an error. See (Xilinx Solution 640) for more


Direct assignments as hex values are not supported in FPGA Express 2.x.
There is a function (To_X01) in std_logic_1164.all to convert.

dout <= to_x01(X"F0");

With FPGA Express 3.0 and newer, the conversion function is not needed:

dout <= X"FO";
AR# 4376
Date 08/31/2001
Status Archive
Type General Article