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VHDL Simulation
Using the TextIO Package
procedure WRITE(L: inout LINE; VALUE: in BIT_VECTOR;
JUSTIFIED: in SIDE:= RIGHT; FIELD: in WIDTH := 0);
procedure WRITE(L: inout LINE; VALUE: in STRING;
JUSTIFIED: in SIDE:= RIGHT; FIELD: in WIDTH := 0);
The error occurs because the argument "hello" could be interpreted as a string or a bit vector,
but the compiler is not allowed to determine the argument type until it knows which function is
being called.
The following procedure call also generates an error:
WRITE (L, "010101");
This call is even more ambiguous, because the compiler could not determine, even if allowed to,
whether the argument "010101" should be interpreted as a string or a bit vector.
There are two possible solutions to this problem:
•
Use a qualified expression to specify the type, as in:
WRITE (L, string’("hello"));
•
Call a procedure that is not overloaded, as in:
WRITE_STRING (L, "hello");
The WRITE_STRING procedure simply defines the value to be a STRING and calls the
WRITE procedure, but it serves as a shell around the WRITE procedure that solves the
overloading problem. For further details, refer to the WRITE_STRING procedure in the io_utils
package, which is located in the file
<install_dir>/modeltech/examples/vhdl/io_utils/io_utils.vhd.
Reading and Writing Hexadecimal Numbers
The reading and writing of hexadecimal numbers is not specified in standard VHDL. The Issues
Screening and Analysis Committee of the VHDL Analysis and Standardization Group (ISACVASG) has specified that the TextIO package reads and writes only decimal numbers.
To expand this functionality, ModelSim supplies hexadecimal routines in the package io_utils,
which is located in the file <install_dir>/modeltech/examples/gui/io_utils.vhd. To use these
routines, compile the io_utils package and then include the following use clauses in your VHDL
source code:
use std.textio.all;
use work.io_utils.all;
ModelSim User’s Manual, v10.1c
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