IEEE Standard for Verilog
Hardware Description Language
®
IEEE Computer Society
Sponsored by the
Design Automation Standards Committee
IEEE
3 Park Avenue
New York, NY 10016-5997, USA
7 April 2006
IEEE Std 1364™-2005
(Revision of IEEE Std 1364-2001)
IEEE Std 1364™-2005
(Revision of IEEE Std 1364-2001)
IEEE Standard for Verilog
Hardware Description Language
Sponsor
®
Design Automation Standards Committee
of the
IEEE Computer Society
Abstract:
The Verilog hardware description language (HDL) is defined in this standard. Verilog
HDL is a formal notation intended for use in all phases of the creation of electronic systems. Be-
cause it is both machine-readable and human-readable, it supports the development, verification,
synthesis, and testing of hardware designs; the communication of hardware design data; and the
maintenance, modification, and procurement of hardware. The primary audiences for this standard
are the implementors of tools supporting the language and advanced users of the language.
Keywords:
computer, computer languages, digital systems, electronic systems, hardware, hard-
ware description languages, hardware design, HDL, PLI, programming language interface, Verilog,
Verilog HDL, Verilog PLI
The Institute of Electrical and Electronics Engineers, Inc.
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Copyright © 2006 by the Institute of Electrical and Electronics Engineers, Inc.
All rights reserved. Published 7 April 2006. Printed in the United States of America.
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Engineers, Incorporated.
Verilog is a registered trademark of Cadence Design Systems, Inc.
Print:
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Introduction
This introduction is not a part of IEEE Std 1364-2005, IEEE Standard for Verilog
®
Hardware Description Language.
The Verilog hardware description language (HDL) became an IEEE standard in 1995 as IEEE Std 1364-
1995. It was designed to be simple, intuitive, and effective at multiple levels of abstraction in a standard
textual format for a variety of design tools, including verification simulation, timing analysis, test analysis,
and synthesis. It is because of these rich features that Verilog has been accepted to be the language of choice
by an overwhelming number of integrated circuit (IC) designers.
Verilog contains a rich set of built-in primitives, including logic gates, user-definable primitives, switches,
and wired logic. It also has device pin-to-pin delays and timing checks. The mixing of abstract levels is
essentially provided by the semantics of two data types: nets and variables. Continuous assignments, in
which expressions of both variables and nets can continuously drive values onto nets, provide the basic
structural construct. Procedural assignments, in which the results of calculations involving variable and net
values can be stored into variables, provide the basic behavioral construct. A design consists of a set of mod-
ules, each of which has an input/output (I/O) interface, and a description of its function, which can be struc-
tural, behavioral, or a mix. These modules are formed into a hierarchy and are interconnected with nets.
The Verilog language is extensible via the programming language interface (PLI) and the Verilog proce-
dural interface (VPI) routines. The PLI/VPI is a collection of routines that allows foreign functions to access
information contained in a Verilog HDL description of the design and facilitates dynamic interaction with
simulation. Applications of PLI/VPI include connecting to a Verilog HDL simulator with other simulation
and computer-assisted design (CAD) systems, customized debugging tasks, delay calculators, and
annotators.
The language that influenced Verilog HDL the most was HILO-2, which was developed at Brunel Univer-
sity in England under a contract to produce a test generation system for the British Ministry of Defense.
HILO-2 successfully combined the gate and register transfer levels of abstraction and supported verification
simulation, timing analysis, fault simulation, and test generation.
In 1990, Cadence Design Systems placed the Verilog HDL into the public domain and the independent
Open Verilog International (OVI) was formed to manage and promote Verilog HDL. In 1992, the Board of
Directors of OVI began an effort to establish Verilog HDL as an IEEE standard. In 1993, the first IEEE
working group was formed; and after 18 months of focused efforts, Verilog became an IEEE standard as
IEEE Std 1364-1995.
After the standardization process was complete, the IEEE P1364 Working Group started looking for feed-
back from IEEE 1364 users worldwide so the standard could be enhanced and modified accordingly. This
led to a five-year effort to get a much better Verilog standard in IEEE Std 1364-2001.
With the completion of IEEE Std 1364-2001, work continued in the larger Verilog community to identify
outstanding issues with the language as well as ideas for possible enhancements. As Accellera began work-
ing on standardizing SystemVerilog in 2001, additional issues were identified that could possibly have led to
incompatibilities between Verilog 1364 and SystemVerilog. The IEEE P1364 Working Group was estab-
lished as a subcomittee of the SystemVerilog P1800 Working Group to help ensure consistent resolution of
such issues. The result of this collaborative work is this standard, IEEE Std 1364-2005.
Copyright © 2006 IEEE. All rights reserved.
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