<PAGE>
EXHIBIT 5.1
OPINION OF COOLEY GODWARD
[LETTERHEAD OF COOLEY GODWARD LLP]
January 12, 2001
Terayon Communication Systems, Inc.
2952 Bunker Hill Lane
Santa Clara, CA 95054
Ladies and Gentlemen:
You have requested our opinion with respect to certain matters in connection
with the filing by Terayon Communication Systems, Inc. (the "Company") of a
Registration Statement on Form S-3 (the "Registration Statement") with the
Securities and Exchange Commission (the "Commission") covering the sale by
certain selling stockholders five hundred thirty four thousand four hundred
eighty seven (534,487) shares of the Company's common stock (the "Selling
Stockholder Shares").
In connection with this opinion, we have examined the Registration Statement,
the Company's Certificate of Incorporation and Bylaws, each as amended, and such
other documents, records, certificates, memoranda and other instruments as we
deem necessary as a basis for this opinion. We have assumed the genuineness and
authenticity of all documents submitted to us as originals, the conformity to
originals of all documents submitted to us as copies thereof, and the due
execution and delivery of all documents where due execution and delivery are a
prerequisite to the effectiveness thereof.
On the basis of the foregoing, and in reliance thereon, we are of the opinion
that the Selling Stockholder Shares are validly issued, fully paid and
nonassessable.
We consent to the reference to our firm under the caption "Legal Matters" in the
Prospectus included in the Registration Statement and to the filing of this
opinion as an exhibit to the Registration Statement.
Very truly yours,
Cooley Godward LLP
By: /s/ Karyn S. Tucker
-------------------------------------
Karyn S. Tucker
