Document:

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                                                                     EXHIBIT 4.2

                          [Form of Rights Certificate]

Certificate No. R-                                             __________ Rights

         NOT EXERCISABLE AFTER DECEMBER 6, 2010 OR EARLIER IF REDEEMED BY THE
         COMPANY. THE RIGHTS ARE SUBJECT TO REDEMPTION, AT THE OPTION OF THE
         COMPANY, AT $0.01 PER RIGHT ON THE TERMS SET FORTH IN THE RIGHTS
         AGREEMENT. UNDER CERTAIN CIRCUMSTANCES, RIGHTS BENEFICIALLY OWNED BY AN
         ACQUIRING PERSON (AS SUCH TERM IS DEFINED IN THE RIGHTS AGREEMENT) AND
         ANY SUBSEQUENT HOLDER OF SUCH RIGHTS MAY BECOME NULL AND VOID. [THE
         RIGHTS REPRESENTED BY THIS RIGHTS CERTIFICATE ARE OR WERE BENEFICIALLY
         OWNED BY A PERSON WHO WAS OR BECAME AN ACQUIRING PERSON OR AN AFFILIATE
         OR ASSOCIATE OF AN ACQUIRING PERSON (AS SUCH TERMS ARE DEFINED IN THE
         RIGHTS AGREEMENT). ACCORDINGLY, THIS RIGHTS CERTIFICATE AND THE RIGHTS
         REPRESENTED HEREBY MAY BECOME NULL AND VOID IN THE CIRCUMSTANCES
         SPECIFIED IN SECTION 7(e) OF SUCH AGREEMENT.](2)

                               Rights Certificate

                             INTERPHASE CORPORATION

         This certifies that                      , or registered assigns, is
the registered owner of the number of Rights set forth above, each of which
entitles the owner thereof, subject to the terms, provisions and conditions of
the Rights Agreement, dated as of December 7, 2000 (the "Rights Agreement"),
between Interphase Corporation, a Texas corporation (the "Company"), and
Computershare Investor Services, LLC, a limited liability company organized
under the laws of the State of Delaware (the "Rights Agent"), to purchase from
the Company at any time prior to 5:00 P.M. (New York City time) on December 6,
2010 at the office or offices of the Rights Agent designated for such purpose,
or its successors as Rights Agent, one fully paid, nonassessable share of Common
Stock (the "Common Stock") of the Company, at a purchase price of $93.00 per
share (the "Purchase Price"), upon presentation and surrender of this Rights
Certificate with the Form of Election to Purchase and related Certificate duly
executed. The

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         (2) The portion of the legend in brackets shall be inserted only if
applicable and shall replace the preceding sentence.

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Purchase Price shall be paid, at the election of the holder, in
cash or shares of Common Stock of the Company having an equivalent value. The
number of Rights evidenced by this Rights Certificate (and the number of shares
which may be purchased upon exercise thereof) set forth above, and the Purchase
Price per share set forth above, are the number and Purchase Price as of
December 7, 2000, based on the Common Stock as constituted at such date.

         Upon the occurrence of the Section 11(a)(ii) Event (as such term is
defined in the Rights Agreement), if the Rights evidenced by this Rights
Certificate are beneficially owned by (i) an Acquiring Person or an Affiliate or
Associate of any such Acquiring Person (as such terms are defined in the Rights
Agreement), (ii) a transferee of any such Acquiring Person, Associate or
Affiliate, or (iii) under certain circumstances specified in the Rights
Agreement, a transferee of a person who, after such transfer, became an
Acquiring Person, or an Affiliate or Associate of an Acquiring Person, such
Rights shall become null and void and no holder hereof shall have any right with
respect to such Rights from and after the occurrence of the Section 11(a)(ii)
Event.

         As provided in the Rights Agreement, the Purchase Price and the number
and kind of shares of Common Stock or other securities, which may be purchased
upon the exercise of the Rights evidenced by this Rights Certificate are subject
to modification and adjustment upon the happening of certain events, including
Triggering Events.

         This Rights Certificate is subject to all of the terms, provisions and
conditions of the Rights Agreement, which terms, provisions and conditions are
hereby incorporated herein by reference and made a part hereof and to which
Rights Agreement reference is hereby made for a full description of the rights,
limitations of rights, obligations, duties and immunities hereunder of the
Rights Agent, which limitations of rights include the temporary suspension of
the exercisability of such Rights under the specific circumstances set forth in
the Rights Agreement. Copies of the Rights Agreement are on file at the
above-mentioned office of the Rights Agent and are also available upon written
request to the Rights Agent.

         This Rights Certificate, with or without other Rights Certificates,
upon surrender at the principal office or offices of the Rights Agent designated
for such purpose, may be exchanged for another Rights Certificate or Rights
Certificates of like tenor and date evidencing Rights entitling the holder to
purchase a like aggregate number of Common Stock as the Rights evidenced by the
Rights Certificate or Rights Certificates surrendered shall have entitled such
holder to purchase. If this Rights Certificate shall be exercised in part, the
holder shall be entitled to receive upon surrender hereof another Rights
Certificate or Rights Certificates for the number of whole Rights not exercised.

         Subject to the provisions of the Rights Agreement, the Rights evidenced
by this Certificate may be redeemed by the Company at its option at a redemption
price of $0.01 per Right at any time prior to the earlier of the close of
business on (i) the tenth Business Day following the Stock Acquisition Date (as
such time period may be extended pursuant to the Rights Agreement), and (ii) the
Final Expiration Date.

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         The Company is not required to issue fractional shares of Common Stock
upon the exercise of any Right or Rights evidenced hereby (other than fractions
which are integral multiples of one share of Common Stock, which may, at the
election of the Company, be evidenced by depositary receipts), but in lieu
thereof a cash payment may be made, as provided in the Rights Agreement.

         No holder of this Rights Certificate shall be entitled to vote or
receive dividends or be deemed for any purpose the holder of shares of Common
Stock or of any other securities of the Company which may at any time be
issuable on the exercise hereof, nor shall anything contained in the Rights
Agreement or herein be construed to confer upon the holder hereof, as such, any
of the rights of a stockholder of the Company or any right to vote for the
election of directors or upon any matter submitted to stockholders at any
meeting thereof, or to give or withhold consent to any corporate action, or to
receive notice of meetings or other actions affecting stockholders (except as
provided in the Rights Agreement), or to receive dividends or subscription
rights, or otherwise, until the Right or Rights evidenced by this Rights
Certificate shall have been exercised as provided in the Rights Agreement.

         This Rights Certificate shall not be valid or obligatory for any
purpose until it shall have been countersigned by the Rights Agent.

         WITNESS the facsimile signature of the proper officers of the Company
and its corporate seal.

Dated as of                 ,
            ----------------  -----

Attest:                                INTERPHASE CORPORATION

By:
   -------------------------------     -----------------------------------

Name:
     -----------------------------     -----------------------------------

Title:
      ----------------------------     -----------------------------------

Countersigned:

COMPUTERSHARE INVESTOR SERVICES, LLC

By:
   ----------------------------------
         Authorized Signature

                                      -3-
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                  [Form of Reverse Side of Rights Certificate]

                               FORM OF ASSIGNMENT

                (To be executed by the registered holder if such
               holder desires to transfer the Rights Certificate.)

FOR VALUE RECEIVED _____________________________________________________________
hereby sells, assigns and transfers unto________________________________________

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                  (Please print name and address of transferee)

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this Rights Certificate, together with all right, title and interest therein,
and does hereby irrevocably constitute and appoint __________________ Attorney,
to transfer the within Rights Certificate on the books of the within-named
Company, with full power of substitution.

Date:                     ,
     ---------------------  ------

                                       -----------------------------------------
                                                       Signature

Signature Guaranteed:

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                                   CERTIFICATE

         The undersigned hereby certifies by checking the appropriate boxes
that:

                  (1) this Rights Certificate [ ] is [ ] is not being sold,
assigned and transferred by or on behalf of a Person who is or was an Acquiring
Person or an Affiliate or Associate of any such Acquiring Person (as such terms
are defined in the Rights Agreement); and

                  (2) after due inquiry and to the best knowledge of the
undersigned, it [ ] did [ ]did not acquire the Rights evidenced by this Rights
Certificate from any Person who is, was or subsequently became an Acquiring
Person or an Affiliate or Associate of an Acquiring Person.

Dated:               ,
      ---------------  ----                 -----------------------------
                                                      Signature

Signature Guaranteed:

                                     NOTICE

                  The signature to the foregoing Assignment and Certificate must
correspond to the name as written upon the face of this Rights Certificate in
every particular, without alteration or enlargement or any change whatsoever.

                                      -5-
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                          FORM OF ELECTION TO PURCHASE

     (To be executed if holder desires to exercise Rights represented by the
                              Rights Certificate.)

To: INTERPHASE CORPORATION

         The undersigned hereby irrevocably elects to exercise ____________
Rights represented by this Rights Certificate to purchase the shares of Common
Stock issuable upon the exercise of the Rights (or such other securities of the
Company or of any other person which may be issuable upon the exercise of the
Rights) and requests that certificates for such shares be issued in the name of
and delivered to:

Please insert social security
or other identifying number
                           ----------------------------------

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                         (Please print name and address)

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         If such number of Rights shall not be all the Rights evidenced by this
Rights Certificate, a new Rights Certificate for the balance of such Rights
shall be registered in the name of and delivered to:

Please insert social security
or other identifying number
                           ----------------------------

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                         (Please print name and address)

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Dated:                     ,
      ---------------------  -----
                                       -----------------------------------------
                                                      Signature

Signature Guaranteed:

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                                   CERTIFICATE

         The undersigned hereby certifies by checking the appropriate boxes
that:

         (1) the Rights evidenced by this Rights Certificate [ ] are [ ] are not
being exercised by or on behalf of a Person who is or was an Acquiring Person or
an Affiliate or Associate of any such Acquiring Person (as such terms are
defined in the Rights Agreement); and

         (2) after due inquiry and to the best knowledge of the undersigned, it
[ ] did [ ] did not acquire the Rights evidenced by this Rights Certificate from
any Person who is, was or became an Acquiring Person or an Affiliate or
Associate of an Acquiring Person.

Dated:                ,
      ----------------  ----           -----------------------------------------
                                                      Signature

Signature Guaranteed:

                                     NOTICE

                  The signature to the foregoing Election to Purchase and
Certificate must correspond to the name as written upon the face of this Rights
Certificate in every particular, without alteration or enlargement or any change
whatsoever.

                                      -7-<PAGE>   1
                                                                     EXHIBIT 4.3

                          SUMMARY OF RIGHTS TO PURCHASE
                                PREFERRED SHARES

         On December 7, 2000 the Board of Directors of Interphase Corporation
(the "Company") declared a dividend of one common share purchase right (a
"Right") for each outstanding share of common stock, par value $0.01 per share
(the "Common Stock"), of the Company. The dividend is payable on December 29,
2000 (the "Record Date"), to the stockholders of record on that date. Each Right
entitles the registered holder to purchase from the Company one share of Common
Stock at a price of $93.00 per share (the "Purchase Price"), subject to
adjustment. The complete description and terms of the Rights are set forth in a
Rights Agreement, dated as of December 7, 2000, as the same may be amended from
time to time (the "Rights Agreement"), between the Company and Computershare
Investor Services, LLC as Rights Agent (the "Rights Agent"). The following
description of the Rights Agreement is a summary of the material terms thereof
and is qualified in its entirety by reference to the complete text of the Rights
Agreement.

         Upon distribution, the Rights will be attached to all outstanding
shares of Common Stock and will be represented by the certificates representing
such shares. No separate certificates evidencing the Rights (the "Rights
Certificates") will be distributed prior to the Distribution Date (as defined
below). The Rights will separate from the Common Stock and a "Distribution Date"
will occur upon the earlier of (i) 10 business days following a public
announcement that a person or group of affiliated or associated persons (an
"Acquiring Person") has acquired, or obtained the right to acquire, beneficial
ownership of 15% or more of the outstanding shares of Common Stock (the "Stock
Acquisition Date"), or (ii) 10 business days (or such later date as the Board of
Directors shall determine) following the commencement of a tender or exchange
offer that would result in a person or group beneficially owning 15% or more of
such outstanding shares of Common Stock (the "Tender Offer Date"). Until the
Distribution Date, (i) the Rights will be evidenced by the Common Stock
certificates and will be transferred with and only with such Common Stock
certificates, (ii) the Common Stock certificates issued after the date of the
Rights Agreement will contain a notation incorporating the Rights Agreement by
reference, and (iii) the surrender for transfer of any certificates for Common
Stock outstanding will also constitute the transfer of the Rights associated
with the Common Stock represented by such certificates. Pursuant to the Rights
Agreement, the Company reserves the right to require prior to the occurrence of
a Triggering Event (as defined below) that, upon any exercise of Rights, a
number of Rights be exercised so that only whole shares of Common Stock will be
issued.

         The Rights are not exercisable until the Distribution Date and will
expire at the close of business on December 6, 2010, or such later date as the
Board of Directors establishes under certain circumstances, unless earlier
redeemed by the Company as described below.

         As soon as practicable after the Distribution Date, Rights Certificates
will be mailed to holders of record of Common Stock as of the close of business
on the Distribution Date and, thereafter, the separate Rights Certificates alone
will represent the Rights. Except as otherwise

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determined by the Board of Directors, only shares of Common Stock outstanding
prior to the Distribution Date will be issued with Rights.

         If any Person becomes the beneficial owner of 15% or more of the then
outstanding shares of Common Stock (unless such acquisition is made pursuant to
a tender or exchange offer for all outstanding shares of Common Stock, upon
terms and conditions determined by a majority of the directors to be in the best
interests of the Company and its stockholders (a "Qualifying Offer")), each
holder of a Right (other than an Acquiring Person, certain related parties and
transferees) will thereafter have the right to receive, upon exercise, Common
Stock (or, in certain circumstances, cash, property or other securities of the
Company), having a value equal to two times the exercise price of the Right. For
example, at an exercise price of $93.00 per Right, each Right not owned by an
Acquiring Person (or by certain related parties or transferees) following the
event set forth above would entitle its holder to purchase $186.00 worth of
Common Stock (or other consideration, as noted above) for $93.00. Assuming that
the Common Stock had a per share market price of $46.50 at such time, the holder
of each valid Right would be entitled to purchase four shares of Common Stock
for $93.00. The Rights are not exercisable following the occurrence of any of
the events described above until such time as the Rights are no longer
redeemable by the Company as described below. Notwithstanding any of the
foregoing, following the occurrence of any of the events set forth in this
paragraph, all Rights that are, or (under certain circumstances specified in the
Rights Agreement) were, beneficially owned by any Acquiring Person will be null
and void.

         If at any time following the Stock Acquisition Date, (i) the Company is
acquired in a merger or business combination transaction in which it is not the
surviving corporation (other than a merger consummated pursuant to a Qualifying
Offer); (ii) the Company is the surviving corporation in a business combination
transaction (other than such a transaction consummated pursuant to a Qualifying
Offer) but all or part of the outstanding shares of Common Stock are changed or
exchanged for stock or other securities of any person or cash or any other
property; or (iii) more than 50% of the Company's combined assets or earning
power is sold or transferred (in each case other than certain consolidations
with, mergers with and into, or sales of assets or earning power by or to
subsidiaries of the Company as specified in the Rights Agreement), each holder
of a Right (except Rights which have previously been voided as set forth above)
shall thereafter have the right to receive, upon exercise thereof, common stock
of the acquiring company having a value equal to two times the exercise price of
the Right. The events described in this paragraph and in the preceding paragraph
are referred to as the "Triggering Events."

         In order to prevent dilution, the Purchase Price payable, the number
and kind of shares covered by each Right and the number of Rights outstanding
are subject to adjustment from time to time (x) in the event of a stock dividend
on, or a subdivision, combination or reclassification of, the Common Stock, (y)
if holders of the Common Stock are granted certain rights or warrants to
subscribe for Common Stock or securities convertible into Common Stock at less
than the current market price of the Common Stock, or (z) upon the distribution
to holders of the Common Stock of evidences of indebtedness, cash (excluding
regular quarterly cash dividends),

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assets (other than dividends payable in Common Stock) or subscription rights or
warrants (other than those referred to in clause (y) above).

         With certain exceptions, no adjustments in the Purchase Price will be
required until cumulative adjustments amount to at least 1% of the Purchase
Price. No fractional shares of Common Stock are required to be issued (other
than fractions which are integral multiples of one share of Common Stock) and,
in lieu thereof, the Company may make an adjustment in cash based on the market
price of the Common Stock on the trading day prior to the date of exercise.

         At any time until ten business days following the Stock Acquisition
Date, the Company may redeem the Rights in whole, but not in part, at a price of
$0.01 per Right (payable in cash, shares of Common Stock or other consideration
deemed appropriate by the Board of Directors). The redemption of the Rights may
be made effective at such time on such basis with such conditions as the Board
of Directors, in its sole discretion, may establish. Immediately upon any
redemption of the Rights, the right to exercise the Rights will terminate and
the only right of the holders of Rights will be to receive the $0.01 redemption
price.

         Until a Right is exercised, the holder thereof, as such, will have no
rights as a stockholder of the Company, including, without limitation, the right
to vote or to receive dividends.

         Any of the provisions of the Rights Agreement may be amended by the
Board of Directors prior to the Distribution Date, other than the redemption
price and the number of shares of Common Stock for which a Right is exercisable,
and the Purchase Price may not be reduced. After the Distribution Date, the
provisions of the Rights Agreement may be amended by the Board of Directors in
order to cure any ambiguity, to make changes which do not adversely affect the
interests of holders of Rights or to shorten or lengthen any time period under
the Rights Agreement, except that no amendment to adjust the time period
governing redemption may be made at such time as the Rights are not redeemable.
The Final Expiration Date (as defined in the Rights Agreement) may be changed
and the Purchase Price may be increased at any time prior to a Stock Acquisition
Date or a Tender Offer Date.

         THIS SUMMARY DESCRIPTION OF THE RIGHTS DOES NOT PURPORT TO BE COMPLETE
AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO THE RIGHTS AGREEMENT, WHICH IS
HEREBY INCORPORATED BY REFERENCE.

A copy of the Rights Agreement has been filed with the Securities and Exchange
Commission as an Exhibit to a Registration Statement on Form 8-A. A copy of the
Rights Agreement is available free of charge from the Company.

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