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AR# 640

FPGA Express 3.x: Expression is ambiguous (VSS-501)


Keywords: Express, Foundation, FPGA, HEX, OCTAL, IEEE, convert, function
std_logic_vector, std_ulogic_vector, To_X01

Urgency: Standard

General Description:
FPGA Express no longer requires conversion functions to convert from
HEX or OCTAL values to std_logic_vectors. These functions are found
in the STD_LOGIC_1164 library and the previous requirements are
described in (Xilinx Solution 4376).

However, the use of these conversion functions will lead to a Synopsys
error when checking syntax:

Error L29/C0 : #0 Error: C:/path/mydesign.vhd line 29
Expression is ambiguous. (VSS-501)

This error is most frequently seen after having upgraded from
FPGA Express v2.x to v3.x.


Remove the explicit call to the conversion function. For example:

dout <= to_stdlogicvector(X"F0");

should be edited to simply:

dout <= (X"F0");

The parenthesis are optional, but are okay to leave in. This
will allow users to globally search and replace the offending
conversion function. "To_X01" is another such conversion.
AR# 640
Date Created 09/20/1995
Last Updated 08/27/2001
Status Archive
Type General Article