<PAGE>   1
                                                                    EXHIBIT 3.1


                        CERTIFICATE OF INCORPORATION

                                     OF


                      U.S. ROBOTICS HOLDING CORPORATION



     1. The name of the Corporation is U.S. ROBOTICS HOLDING CORPORATION.


     2. The address of the registered office in the State of Delaware is 1209
Orange Street in the City of Wilmington, County of New Castle.  The name of its
registered agent at such address is The Corporation Trust Company.


     3. The nature of the business or purposes to be conducted or promoted is to
engage in any lawful act or activity for which corporations may be organized
under the General Corporation Law of Delaware.


     4. Capitalization.  The total number of shares of stock which the
Corporation shall have authority to issue is eighty million (80,000,000), of
which seventy-five million (75,000,000) shares, of the par value of One Cent
($0.01) each, shall be common stock and five million (5,000,000) shares, of the
par value of One Cent ($0.01) each, shall be preferred stock; preferred stock
shall be issued from time to time (a) in one or more series with such
distinctive serial designations; and (b) may have such voting powers, full or
limited, or may be without voting powers; and (c) may be subject to redemption
at such time or times and at such prices; and (d) may be entitled to receive
dividends (which may be cumulative or noncumulative) at such rate or rates, on
such conditions, and at such times, and payable in preference to, or in such
relation to, the dividends payable on any other class or classes of stock; and
(e) may have such rights upon the dissolution of, or upon any distribution of
the assets of, the Corporation; and (f) may be made convertible into, or
exchangeable for, shares of any other class or classes or of any other series of
the same or any other class or classes of stock of the Corporation, at such
price or prices or at such rates of exchange, and with such adjustments; and (g)
shall have such other relative, participating, optional or other special rights
and qualifications, limitations or restrictions thereof, all as shall hereafter
be stated and expressed in the resolution or resolutions providing for the issue
of such preferred stock from time to time adopted by the Board of Directors
pursuant to authority to do so which is hereby vested in the Board.

     5. The name and mailing address of the incorporator is: Daniel G. Kazan,
190 South LaSalle Street, Chicago, Illinois 60603.

     6. In furtherance and not in limitation of the powers conferred by the
laws of the State of Delaware, the Board of Directors is expressly authorized
to adopt, amend or repeal the By-laws of the Corporation.

     7. The business and affairs of the Corporation shall be managed by the
Board of Directors, and the directors need not be elected by written ballot
unless the By-laws so provide. 

     8. The Corporation reserves the right to amend, alter, change or repeal
any provisions contained in this Certificate of Incorporation in the manner now
or hereafter prescribed by law, and all the provisions of this Certificate of
Incorporation and all rights and powers conferred in this Certificate of
Incorporation on stockholders, directors and officers are subject to this
reserved power, provided
<PAGE>   2


that the affirmative vote of the holders of record of outstanding shares
representing at least eighty percent (80%) of the voting power of all of the
shares of capital stock of the Corporation then entitled to vote generally in
the election of directors, voting together as a single class, shall be required
to amend, alter, change or repeal any provision of, or to adopt any provision or
provisions inconsistent with this Section 8 of the Certificate of Incorporation
or Article III, Sections 2 and 14 of the By-laws unless such amendment,
alteration, repeal or adoption of any inconsistent provision or provisions is
declared advisable by the Board of Directors by the affirmative vote of at least
seventy-five percent (75%) of the entire Board of Directors, notwithstanding the
fact that a lesser percentage may be specified by the General Corporation Law of
Delaware.


     9. A director of this Corporation shall not be personally liable to the
Corporation or its stockholders for monetary damages for breach of fiduciary
duty as a director, except for liability (i) for any breach of the director's
duty of loyalty to the Corporation or its stockholders, (ii) for acts or
omissions not in good faith or which involve intentional misconduct or a knowing
violation of law, (iii) under Section 174 of the Delaware General Corporation
Law, or (iv) for any transaction from which the director derived an improper
personal benefit.


     I, THE UNDERSIGNED, being the incorporator hereinbefore named, for the
purpose of forming a corporation pursuant to the General Corporation Law of the
State of Delaware, do make this certificate, hereby declaring and certifying
that this is my act and deed and the facts herein stated are true, and
accordingly have hereunto set my hand this 29th day of November, 1994.



                                     /s/ Daniel G. Kazan
                                     -------------------

                                     Sole Incorporator




                                     -2-

<PAGE>   3
                          CERTIFICATE OF DESIGNATIONS

                                       of


                     SERIES A PARTICIPATING PREFERRED STOCK


                                       of


                       U.S. ROBOTICS HOLDING CORPORATION


                        (Pursuant to Section 151 of the

                       Delaware General Corporation Law)

                       --------------------------------


          U.S. Robotics Holding Corporation, a corporation organized and
existing under the General Corporation Law of the State of Delaware (hereinafter
called the "Corporation"), hereby certifies that the following resolution was
adopted by the Board of Directors of the Corporation as required by Section
141(f) of the General Corporation Law by a written consent dated January 10,
1995.


          RESOLVED, that pursuant to the authority granted to and vested in the
Board of Directors of this Corporation (hereinafter called the "Board of
Directors" or the "Board") in accordance with the provisions of the Certificate
of Incorporation, the Board of Directors hereby creates a series of Preferred
Stock, par value $0.01 per share (the "Preferred Stock"), of the Corporation and
hereby states the designation and number of shares, and fixes the relative
rights, preferences, and limitations thereof as follows:


          Series A Participating Preferred Stock:

          Section 1.  Designation and Amount.  The shares of such series shall
be designated as "Series A Participating Preferred Stock" (the "Series A
Preferred Stock") and the number of shares constituting the Series A Preferred
Stock shall be 750,000.  Such number of shares may be increased or decreased by
resolution of the Board of Directors; provided, that no decrease shall reduce
the number of shares of Series A Preferred Stock to a number less than the
number of shares then outstanding plus the number of shares reserved for
issuance upon the exercise of outstanding options, rights or warrants or upon
the conversion of any outstanding securities issued by the Corporation
convertible into Series A Preferred Stock.


          Section 2.  Dividends and Distributions.


          (A) The holders of shares of Series A Preferred Stock, in preference
     to the holders of Common Stock, par value $.01 per share (the "Common
     Stock"), of the Corporation, and of any other junior stock, shall be
     entitled to receive, when, as and if declared by the Board of Directors out
     of funds legally available for the purpose, quarterly dividends payable in
     cash on the first day of March, June, September and December in each year
     (each such date being referred to herein as a "Quarterly Dividend Payment
     Date"), commencing on the first Quarterly Dividend Payment Date after the
     first issuance of a share or fraction of a share of Series A Preferred
     Stock, in an amount per share (rounded to the nearest cent) equal to the
     greater of (a) $1.00 or (b) subject to the provision for adjustment
     hereinafter set forth, 100 times the aggregate per share amount of all cash
     dividends, and 100 times the aggregate per share amount (payable in kind)
     of all non-cash dividends or other distributions, other than a dividend
     payable in shares of Common Stock or a subdivision of the outstanding
     shares of Common Stock (by reclassification or otherwise), declared on the
     Common Stock since the immediately preceding Quarterly Dividend Payment
     Date or, with respect to the first Quarterly Dividend Payment Date, since
     the first issuance of any share or fraction of a share of Series A
     Preferred Stock.  In the event the Corporation shall at any time declare or
     pay any dividend on the Common Stock payable in shares of Common Stock, or
     effect a subdivision or combination or consolidation

<PAGE>   4
     of the outstanding shares of Common Stock (by reclassification or otherwise
     than by payment of a dividend in shares of Common Stock), then in each such
     case the amount to which holders of shares of Series A Preferred Stock were
     entitled immediately prior to such event under clause (b) of the preceding
     sentence shall be adjusted by multiplying such amount by a fraction, the
     numerator of which is the number of shares of Common Stock outstanding
     immediately after such event and the denominator of which is the number of
     shares of Common Stock that were outstanding immediately prior to such
     event.

          (B) The Corporation shall declare a dividend or distribution on the
     Series A Preferred Stock as provided in paragraph (A) of this Section
     immediately after it declares a dividend or distribution of the Common
     Stock (other than a dividend payable in shares of Common Stock); provided
     that, in the event no dividend or distribution shall have been declared on
     the Common Stock during the period between any Quarterly Dividend Payment
     Date and the next subsequent Quarterly Dividend Payment Date, a dividend of
     $1.00 per share on the Series A Preferred Stock shall nevertheless be
     payable on such subsequent Quarterly Dividend Payment Date.

          (C) Dividends shall begin to accrue and be cumulative on outstanding
     shares of Series A Preferred Stock from the Quarterly Dividend Payment Date
     next preceding the date of issue of such shares, unless the date of issue
     of such shares is prior to the record date for the first Quarterly Dividend
     Payment Date, in which case dividends on such shares shall begin to accrue
     from the date of issue of such shares, or unless the date of issue is a
     Quarterly Dividend Payment Date or is a date after the record date for the
     determination of holders of shares of Series A Preferred Stock entitled to
     receive a quarterly dividend and before such Quarterly Dividend Payment
     Date, in either of which events such dividends shall begin to accrue and be
     cumulative from such Quarterly Dividend Payment Date.  Accrued but unpaid
     dividends shall not bear interest.  Dividends paid on the shares of Series
     A Preferred Stock in an amount less than the total amount of such dividends
     at the time accrued and payable on such shares shall be allocated pro rata
     on a share-by-share basis among all such shares at the time outstanding.
     The Board of Directors may fix a record date for the determination of
     holders of shares of Series A Preferred Stock entitled to receive payment
     of a dividend or distribution declared thereon, which record date shall be
     not more than 60 days prior to the date fixed for the payment thereof.

          Section 3.  Voting Rights.  The holders of shares of Series A
Preferred Stock shall have the following voting rights:

          (A) Subject to the provision for adjustment hereinafter set forth,
     each share of Series A Preferred Stock shall entitle the holder thereof to
     100 votes on all matters submitted to a vote of the stockholders of the
     Corporation.  In the event the Corporation shall at any time declare or pay
     any dividend on the Common Stock payable in shares of Common Stock, or
     effect a subdivision or combination or consolidation of the outstanding
     shares of Common Stock (by reclassification or otherwise than by payment of
     a dividend in shares of Common Stock) into a greater or lesser number of
     shares of Common Stock, then in each such case the number of votes per
     share to which holders of shares of Series A Preferred Stock were entitled
     immediately prior to such event shall be adjusted by multiplying such
     number by a fraction, the numerator of which is the number of shares of
     Common Stock outstanding immediately after such event and the denominator
     of which is the number of shares of Common Stock that were outstanding
     immediately prior to such event.

          (B) Except as otherwise provided herein, in the Certificate of
     Incorporation, in any other Certificate of Designations creating a series
     of Preferred Stock or any similar stock, or by law, the holders of shares
     of Common Stock and any other capital stock of the Corporation having
     general voting rights shall vote together as one class on all matters
     submitted to a vote of stockholders of the Corporation.



                                      -2-

<PAGE>   5
          (C) Except as set forth herein, or as otherwise provided by the
     Certificate of Incorporation or by law, holders of Series A Preferred Stock
     shall have no special voting rights and their consent shall not be required
     (except to the extent they are entitled to vote with holders of Common
     Stock as set forth herein) for taking any corporate action.

     Section 4.  Certain Restrictions.

          (A) Whenever quarterly dividends or other dividends or distributions
     payable on the Series A Preferred Stock as provided in Section 2 are in
     arrears, thereafter and until all accrued and unpaid dividends and
     distributions, whether or not declared, on shares of Series A Preferred
     Stock outstanding shall have been paid in full, the Corporation shall not:

               (i) declare or pay dividends, or make any other distributions, on
          any shares of stock ranking junior (either as to dividends or upon
          liquidation, dissolution or winding up) to the Series A Preferred
          Stock;

               (ii) declare or pay dividends, or make any other distributions,
          on any shares of stock ranking on a parity (either as to dividends or
          upon liquidation, dissolution or winding up) with the Series A
          Preferred Stock, except dividends paid ratably on the Series A
          Preferred Stock and all such parity stock on which dividends are
          payable or in arrears in proportion to the total amounts to which the
          holders of all such shares are then entitled;

               (iii)  redeem or purchase or otherwise acquire for consideration
          shares of any stock ranking junior (either as to dividends or upon
          liquidation, dissolution or winding up) to the Series A Preferred
          Stock, provided that the Corporation may at any time redeem, purchase
          or otherwise acquire shares of any such junior stock in exchange for
          shares of any stock of the Corporation ranking junior (either as to
          dividends or upon dissolution, liquidation or winding up) to the
          Series A Preferred Stock; or

               (iv) redeem or purchase or otherwise acquire for consideration
          any shares of Series A Preferred Stock, or any shares of stock ranking
          on a parity with the Series A Preferred Stock, except in accordance
          with a purchase offer made in writing or by publication (as determined
          by the Board of Directors) to all holders of such shares upon such
          terms as the Board of Directors, after consideration of the respective
          annual dividend rates and other relative rights and preferences of the
          respective series and classes, shall determine in good faith will
          result in fair and equitable treatment among the respective series or
          classes.

          (B) The Corporation shall not permit any subsidiary of the Corporation
     to purchase or otherwise acquire for consideration any shares of stock of
     the Corporation unless the Corporation could, under paragraph (A) of this
     Section 4, purchase or otherwise acquire such shares at such time and in
     such manner.

          Section 5.  Reacquired Shares.  Any shares of Series A Preferred Stock
purchased or otherwise acquired by the Corporation in any manner whatsoever
shall be retired and cancelled promptly after the acquisition thereof.  All such
shares shall upon their cancellation become authorized but unissued shares of
Preferred Stock and may be reissued as part of a new series of Preferred Stock
subject to the conditions and restrictions on issuance set forth herein, in the
Certificate of Incorporation or in any other Certificate of Designations
creating a series of Preferred Stock or any similar stock or as otherwise
required by law.

          Section 6.  Liquidation, Dissolution or Winding Up.  Upon any
liquidation, dissolution or winding up of the Corporation, no distribution shall
be made (1) to the holders of shares of stock ranking junior (either as to
dividends or upon liquidation, dissolution or winding up) to the Series A
Preferred Stock unless, prior thereto, the holders of shares of Series A
Preferred Stock shall have received $100 per share, plus an amount equal to
accrued and unpaid dividends and distributions thereon, whether or


                                      -3-

<PAGE>   6

not declared, to the date of such payment, provided that the holders of shares
of Series A Preferred Stock shall be entitled to receive an aggregate amount per
share, subject to the provision for adjustment hereinafter set forth, equal to
100 times the aggregate amount to be distributed per share to holders of shares
of Common Stock, or (2) to the holders of shares of stock ranking on a parity
(either as to dividends or upon liquidation, dissolution or winding up) with the
Series A Preferred Stock, except distributions made ratably on the Series A
Preferred Stock and all such parity stock in proportion to the total amounts to
which the holders of all such shares are entitled upon such liquidation,
dissolution or winding up.  In the event the Corporation shall at any time
declare or pay any dividend on the Common Stock payable in shares of Common
Stock, or effect a subdivision or combination or consolidation of the
outstanding shares of Common Stock (by reclassification or otherwise than by
payment of a dividend in shares of Common Stock) into a greater or lesser number
of shares of Common Stock, then in each such case the aggregate amount to which
holders of shares of Series A Preferred Stock were entitled immediately prior to
such event under the proviso in clause (1) of the preceding sentence shall be
adjusted by multiplying such amount by a fraction the numerator of which is the
number of shares of Common Stock outstanding immediately after such event and
the denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.


          Section 7.  Consolidation, Merger, etc.  In case the Corporation shall
enter into any consolidation, merger, combination or other transaction in which
the shares of Common Stock are exchanged for or changed into other stock or
securities, cash and/or any other property, then in any such case each share of
Series A Preferred Stock shall at the same time be similarly exchanged or
changed into an amount per share, subject to the provision for adjustment
hereinafter set forth, equal to 100 times the aggregate amount of stock,
securities, cash and/or any other property (payable in kind), as the case may
be, into which or for which each share of Common Stock is changed or exchanged.
In the event the Corporation shall at any time declare or pay any dividend on
the Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the amount set forth in the preceding sentence with respect to the
exchange or change of shares of Series A Preferred Stock shall be adjusted by
multiplying such amount by a fraction, the numerator of which is the number of
shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.


          Section 8.  No Redemption.  The shares of Series A Preferred Stock
shall not be redeemable.


          Section 9.  Amendment.  The Certificate of Incorporation of the
Corporation shall not be amended in any manner which would materially alter or
change the powers, preferences or special rights of the Series A Preferred Stock
so as to affect them adversely without the affirmative vote of the holders of at
least two thirds of the outstanding shares of Series A Preferred Stock, voting
together as a single class.



                                      -4-

<PAGE>   7
          IN WITNESS WHEREOF, this Certificate of Designations is executed on
behalf of the Corporation by its Executive Vice President and attested by its
Secretary as of this 23rd day of January, 1995.


                              U.S. ROBOTICS HOLDING CORPORATION,
                              a Delaware corporation



                              By: /s/ Jonathan N. Zakin
                                  ---------------------------
                              Name:   Jonathan N. Zakin
                                      Title: Executive Vice President



ATTEST:




/s/ George A. Vinyard
------------------------------
Name:  George A. Vinyard
Title: Secretary



                                      -5-
<PAGE>   8

                            CERTIFICATE OF AMENDMENT

                                       TO

                          CERTIFICATE OF INCORPORATION

                                       OF

                       U.S. ROBOTICS HOLDING CORPORATION

                       ---------------------------------

                         Adopted in accordance with the
        provisions of Section 242 of the General Corporation Law of the
                               State of Delaware

                       ---------------------------------

     The undersigned, U.S. ROBOTICS HOLDING CORPORATION, a Delaware
corporation, does hereby certify as follows:

     FIRST:  That the name of the corporation is U.S. ROBOTICS HOLDING
CORPORATION.

     SECOND:  That Article 1 of the Certificate of Incorporation of the
Corporation has been amended to read as follows:  The name of the Corporation
is U.S. ROBOTICS CORPORATION.

     THIRD:  That such amendment has been duly adopted in accordance with the
provisions of Section 242 and 228 of the General Corporation Law of the State
of Delaware.

     IN WITNESS WHEREOF, U.S. ROBOTICS HOLDING CORPORATION has caused this
Certificate of Amendment to be executed this 22nd day of February, 1995.


                              U.S. ROBOTICS HOLDING CORPORATION


                              By:  /s/ George A. Vinyard 
                                   -----------------------------
                              Its:  Vice President and Secretary
<PAGE>   9
                            CERTIFICATE OF AMENDMENT
                                       TO
                          CERTIFICATE OF INCORPORATION
                                       OF
                           U.S. ROBOTICS CORPORATION

                         _____________________________

                         Adopted in accordance with the
                        provisions of Section 242 of the
                         General Corporation Law of the
                               State of Delaware
                         _____________________________

     The undersigned, U.S. ROBOTICS CORPORATION, a Delaware corporation, does
hereby certify as follows:

     FIRST:  That the name of the Corporation is U.S. ROBOTICS CORPORATION.

     SECOND:  That Article 4 of the Certificate of Incorporation of the
Corporation has been amended in its entirety to read as follows:

           4. Capitalization. The total number of shares of stock which
      the Corporation shall have authority to issue is two hundred sixty
      million (260,000,000), of which two hundred fifty million
      (250,000,000) shares, of the par value of one cent ($0.01) each,
      shall be common stock and ten million (10,000,000) shares, of the
      par value of one cent ($0.01) each, shall be preferred stock;
      preferred stock (a) may be issued from time to time in one or more
      series with such distinctive serial designations; and (b) may have
      such voting powers, full or limited, or may be without voting
      powers; and (c) may be subject to redemption at such time or times
      and at such prices; and (d) may be entitled to receive dividends
      (which may be cumulative or noncumulative) at such rate or rates,
      on such conditions, and at such times, and payable in preference
      to, or in such relation to, the dividends payable on any other
      class or classes of stock; and (e) may have such rights upon the
      dissolution of, or upon any distribution of the assets of, the
      Corporation; and (f) may be made convertible into, or exchangeable
      for, shares of any other class or classes or of any other series
      of the same or any other class or classes of stock of the
      Corporation, at such price or prices or at such rates of exchange,
      and with such adjustments; and (g) may have such other relative,
      participating, optional or other special rights and
      qualifications, limitations or restrictions thereof, all as shall
      hereafter be stated and expressed in the resolution or resolutions
      providing for the issuance of such preferred stock from time to
      time adopted by the Board of Directors pursuant to the authority to do
      so which is hereby vested in the Board.

     THIRD:  That such amendment has been duly adopted in accordance with the
provisions of Section 242 of the General Corporation Law of the State of
Delaware.
<PAGE>   10


     IN WITNESS WHEREOF, U.S. ROBOTICS CORPORATION has caused this Certificate
of Amendment to be executed this 7th day of March, 1995.

              
                                 U.S. ROBOTICS CORPORATION


                                 By:  /s/ George A. Vinyard
                                      ----------------------------
                                      George A. Vinyard,
                                      Vice President and Secretary


<PAGE>   11

               CERTIFICATE OF DESIGNATION, PREFERENCES AND RIGHTS

                OF SERIES B JUNIOR PARTICIPATING PREFERRED STOCK

                                       of

                           U.S. ROBOTICS CORPORATION

     Pursuant to Section 151 of the General Corporation Law of the State of
Delaware:

     We, Casey Cowell, Chairman, President and Chief Executive Officer, and
George A. Vinyard, Secretary of U.S. Robotics Corporation, a corporation
organized and existing under the General Corporation Law of the State of
Delaware (the "Corporation"), in accordance with the provisions of Section 103
thereof, DO HEREBY CERTIFY:

     That pursuant to the authority conferred upon the Board of Directors by
the Certificate of Incorporation, as amended, of the Corporation, the Board of
Directors on May 9, 1996 adopted the following resolution creating a series of
2,500,000 shares of preferred stock designated as Series B Junior Participating
Preferred Stock:

     RESOLVED, that pursuant to the authority vested in the Board of Directors
of the Corporation in accordance with the provisions of its Certificate of
Incorporation, as amended, a series of preferred stock, par value $.01 per
share, of the Corporation (such preferred stock being herein referred to as
"Preferred Stock," which term shall include any additional shares of preferred
stock of the same class heretofore or hereafter authorized to be issued by the
Corporation), consisting of 2,500,000 shares is hereby created, and the voting
powers, preferences and relative, participating, optional or other special
rights, and the qualifications, limitations or restrictions thereof, are as
follows:

S1. Designation and Amount.  There shall be a series of Preferred Stock of the
Corporation which shall be designated as "Series B Junior Participating
Preferred Stock," par value $.01 per share (hereinafter called "Series B
Preferred Stock"), and the number of shares constituting such series shall be
2,500,000.  Such number of shares may be increased or decreased by resolution
of the Board of Directors and by the filing of a certificate pursuant to the
provisions of the General Corporation Law of the State of Delaware stating that
such increase or reduction has been so authorized; provided, however, that no
decrease shall reduce the number of shares of Series B Preferred Stock to a
number less than that of the shares then outstanding plus the number of shares
of Series B Preferred Stock issuable upon exercise of outstanding rights,
options or warrants or upon conversion of outstanding securities issued by the
Corporation.


                                     -1-
<PAGE>   12


S2. Dividends and Distributions.

     (A) Subject to the prior and superior rights of the holders of any shares
of any series of Preferred Stock ranking prior and superior to the shares of
Series B Preferred Stock with respect to dividends, the holders of shares of
Series B Preferred Stock shall be entitled to receive, when, as and if declared
by the Board of Directors out of funds legally available for the purpose,
quarterly dividends payable in cash to holders of record on the last business
day of March, June, September and December in each year (each such date being
referred to herein as a "Quarterly Dividend Payment Date"), commencing on the
first Quarterly Dividend Payment Date after the first issuance of a share or
fraction of a share of Series B Preferred Stock, in an amount per share
(rounded to the nearest cent) equal to the greater of (a) $1.00 or (b) subject
to the provision for adjustment hereinafter set forth, 100 times the aggregate
per share amount of all cash dividends, and 100 times the aggregate per share
amount (payable in kind) of all non-cash dividends or other distributions other
than a dividend payable in shares of Common Stock (hereinafter defined) or a
subdivision of the outstanding shares of Common Stock (by reclassification or
otherwise), declared on the Common Stock, par value $.01 per share, of the
Corporation (the "Common Stock") since the immediately preceding Quarterly
Dividend Payment Date, or, with respect to the first Quarterly Dividend Payment
Date, since the first issuance of any share or fraction of a share of Series B
Preferred Stock.  In the event the Corporation shall at any time following May
31, 1996 (i) declare any dividend on Common Stock payable in shares of Common
Stock, (ii) subdivide the outstanding Common Stock or (iii) combine the
outstanding Common Stock into a smaller number of shares, then in each such
case the amount to which holders of shares of Series B Preferred Stock were
entitled immediately prior to such event under clause (b) of the preceding
sentence shall be adjusted by multiplying each such amount by a fraction the
numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event.

     (B) The Corporation shall declare a dividend or distribution on the Series
B Preferred Stock as provided in paragraph (A) above at the time it declares a
dividend or distribution on the Common Stock (other than a dividend payable in
shares of Common Stock).

     (C) No dividend or distribution (other than a dividend payable in shares
of Common Stock) shall be paid or payable to the holders of shares of Common
Stock unless, prior thereto, all accrued but unpaid dividends to the date of
such dividend or distribution shall have been paid to the holders of shares of
Series B Preferred Stock.

                                     -2-

<PAGE>   13


     (D) Dividends shall begin to accrue and be cumulative on outstanding
shares of Series B Preferred Stock from the Quarterly Dividend Payment Date
next preceding the date of issue of such shares of Series B Preferred Stock,
unless the date of issue of such shares is prior to the record date for the
first Quarterly Dividend Payment Date, in which case dividends on such shares
shall begin to accrue from the date of issue of such shares, or unless the date
of issue is a Quarterly Dividend Payment Date or is a date after the record
date for the determination of holders of shares of Series B Preferred Stock
entitled to receive a quarterly dividend and before such Quarterly Dividend
Payment Date, in either of which events such dividends shall begin to accrue
and be cumulative from such Quarterly Dividend Payment Date.  Accrued but
unpaid dividends shall not bear interest.  Dividends paid on the shares of
Series B Preferred Stock in an amount less than the total amount of such
dividends at the time accrued and payable on such shares shall be allocated pro
rata on a share-by-share basis among all such shares at the time outstanding.
The Board of Directors may fix a record date for the determination of holders
of shares of Series B Preferred Stock entitled to receive payment of a dividend
or distribution declared thereon, which record date shall be no more than 30
days prior to the date fixed for the payment thereof.

S3. Voting Rights.  The holders of shares of Series B Preferred Stock shall
have the following voting rights:

     (A) Subject to the provision for adjustment hereinafter set forth, each
one one-hundredth of a share of Series B Preferred Stock shall entitle the
holder thereof to one vote on all matters submitted to a vote of the
stockholders of the Corporation.  In the event the Corporation shall at any
time following May 31, 1996 (i) declare any dividend on Common Stock payable in
shares of Common Stock, (ii) subdivide the outstanding shares of Common Stock
or (iii) combine the outstanding Common Stock into a smaller number of shares,
then in each such case the number of votes per share to which holders of shares
of Series B Preferred Stock were entitled immediately prior to such event shall
be adjusted by multiplying such number by a fraction the numerator of which is
the number of shares of Common Stock outstanding immediately after such event
and the denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.
        
     (B) Except as otherwise provided herein or by law, the holders of shares
of Series B Preferred Stock and the holders of shares of Common Stock and any
other capital stock of the Corporation having general voting rights shall vote
together as one class on all matters submitted to a vote of stockholders of the
Corporation.

     (C) (i) Whenever, at any time or times, dividends payable on any share or
     shares of Series B Preferred Stock shall be in arrears in an amount equal
     to at least six full quarterly dividends (whether or not declared and
     whether or not consecutive), the holders of record of the outstanding
     Preferred Stock shall have the exclusive right, voting separately as a
     single class, to elect two directors of the Corporation at a special
     meeting of stockholders of the Corporation or at the Corporation's next
     annual meeting of stockholders, and at each subsequent annual meeting of
     stockholders, as provided below.  At elections for such directors, the
     holders of shares of Series B Preferred Stock shall be entitled to cast one
     vote for each one one-hundredth of a share of Series B Preferred Stock
     held.

          (i) Upon the vesting of such right of the holders of the Preferred
     Stock, the maximum authorized number of members of the Board of Directors
     shall automatically be increased by two and the two vacancies so created
     shall be filled by vote of the holders of the outstanding Preferred Stock
     as hereinafter

                                     -3-

<PAGE>   14


      set forth.  A special meeting of the stockholders of the
      Corporation then entitled to vote shall be called by the Chairman or the
      President or the Secretary of the Corporation, if requested in writing by
      the holders of record of not less than 10% of the Preferred Stock then
      outstanding.  At such special meeting, or, if no such special meeting
      shall have been called, then at the next annual meeting of stockholders
      of the Corporation, the holders of the shares of the Preferred Stock
      shall elect, voting as above provided, two directors of the Corporation
      to fill the aforesaid vacancies created by the automatic increase in the
      number of members of the Board of Directors.  At any and all such
      meetings for such election, the holders of a majority of the outstanding
      shares of the Preferred Stock shall be necessary to constitute a quorum
      for such election, whether present in person or by proxy, and such two
      directors shall be elected by the vote of at least a plurality of shares
      held by such stockholders present or represented at the meeting.  Any
      director elected by holders of shares of the Preferred Stock pursuant to
      this Section may be removed at any annual or special meeting, by vote of
      a majority of the stockholders voting as a class who elected such
      director, with or without cause.  In case any vacancy shall occur among
      the directors elected by the holders of the Preferred Stock pursuant to
      this Section, such vacancy may be filled by the remaining director so
      elected, or his successor then in office, and the director so elected to
      fill such vacancy shall serve until the next meeting of stockholders for
      the election of directors.  After the holders of the Preferred Stock
      shall have exercised their right to elect Directors in any default period
      and during the continuance of such period, the number of Directors shall
      not be further increased or decreased except by vote of the holders of
      Preferred Stock as herein provided or pursuant to the rights of any
      equity securities ranking senior to or pari passu with the Series B
      Preferred Stock.

           (ii) The right of the holders of the Preferred Stock, voting
      separately as a class, to elect two members of the Board of Directors of
      the Corporation as aforesaid shall continue until, and only until, such
      time as all arrears in dividends (whether or not declared) on the
      Preferred Stock shall have been paid or declared and set apart for
      payment, at which time such right shall terminate, except as herein or by
      law expressly provided, subject to revesting in the event of each and
      every subsequent default of the character above-mentioned.  Upon any
      termination of the right of the holders of the shares of the Preferred
      Stock as a class to vote for directors as herein provided, the term of
      office of all directors then in office elected by the holders of
      Preferred Stock pursuant to this Section shall terminate immediately.
      Whenever the term of office of the directors elected by the holders of
      the Preferred Stock pursuant to this Section shall terminate and the
      special voting powers vested in the holders of the Preferred Stock
      pursuant to this Section shall have expired, the maximum number of
      members of the Board of Directors of the Corporation shall be such number
      as may be provided for in the By-laws of the Corporation irrespective of
      any increase made pursuant to the provisions of this Section.

     (D) Except as set forth herein, holders of Series B Preferred Stock shall
have no special voting rights and their consent shall not be required (except
to the extent they are entitled to vote with holders of Common Stock as set
forth herein) for taking any corporate action.

S4. Certain Restrictions.

     (A) Whenever quarterly dividends or other dividends or distributions
payable on the Series B Preferred Stock as provided in Section 2 are in
arrears, thereafter and until all accrued and unpaid dividends and
distributions, whether or not declared,

                                     -4-

<PAGE>   15

on shares of Series B Preferred Stock outstanding shall have been paid in full,
the Corporation shall not:

           (i) declare or pay dividends on, make any other distributions on, or
      redeem or purchase or otherwise acquire for consideration any shares of
      stock ranking junior (either as to dividends or upon liquidation,
      dissolution or winding up) to the Series B Preferred Stock;

           (ii) declare or pay dividends on or make any other distributions on
      any shares of stock ranking on a parity (either as to dividends or upon
      liquidation, dissolution or winding up) with the Series B Preferred
      Stock, except dividends paid ratably on the Series B Preferred Stock and
      all such parity stock on which dividends are payable or in arrears in
      proportion to the total amounts to which the holders of all such shares
      are then entitled;

           (iii) redeem or purchase or otherwise acquire for consideration
      shares of any stock ranking on a parity (either as to dividends or upon
      liquidation, dissolution or winding up) with the Series B Preferred
      Stock, provided that the Corporation may at any time redeem, purchase or
      otherwise acquire shares of any such parity stock in exchange for shares
      of any stock of the Corporation ranking junior (either as to dividends or
      upon dissolution, liquidation or winding up) to the Series B Preferred
      Stock; or

           (iv) purchase or otherwise acquire for consideration any shares of
      Series B Preferred Stock, except in accordance with a purchase offer made
      in writing or by publication (as determined by the Board of Directors) to
      all holders of such shares upon such terms as the Board of Directors,
      after consideration of the respective annual dividend rates and other
      relative rights and preferences of the respective series and classes,
      shall determine in good faith will result in fair and equitable treatment
      among the respective series or classes.

     (B) The Corporation shall not permit any subsidiary of the Corporation to
purchase or otherwise acquire for consideration any shares of stock of the
Corporation unless the Corporation could, under paragraph (A) of this Section,
purchase or otherwise acquire such shares at such time and in such manner.

S5. Reacquired Shares.  Any shares of Series B Preferred Stock purchased or
otherwise acquired by the Corporation in any manner whatsoever shall be retired
and cancelled promptly after the acquisition thereof.  All such shares shall
upon their cancellation become authorized but unissued shares of Preferred
Stock and may be reissued as part of a new series of Preferred Stock to be
created by resolution or resolutions of the Board of Directors, subject to the
conditions and restrictions on issuance set forth herein.

S6. Liquidation, Dissolution or Winding Up.  (A)  Upon any voluntary
liquidation, dissolution or winding up of the Corporation, no distribution
shall be made to the holders of shares of stock ranking junior (either as to
dividends or upon liquidation, dissolution or winding up) to the Series B
Preferred Stock unless, prior thereto, the holders of shares of Series B
Preferred Stock shall have received $1.00 per share, plus an amount equal to
accrued and unpaid dividends and distributions thereon, whether or not
declared, to the date of such payment (the "Series B Liquidation Preference").
Following the payment of the full amount of the Series B Liquidation
Preference, no additional distributions shall be made to the holders of shares
of Series B Preferred Stock unless, prior thereto, the holders of shares of
Common Stock shall have received an amount per share (the "Common Adjustment")
equal to the

                                     -5-

<PAGE>   16

quotient obtained by dividing (i) the Series B Liquidation Preference by (ii)
100 (as appropriately adjusted as set forth in subparagraph C below to reflect
such events as stock splits, stock dividends and recapitalizations with respect
to the Common Stock) (such number in clause (ii), the "Adjustment Number").
Following the payment of the full amount of the Series B Liquidation Preference
and the Common Adjustment in respect of all outstanding shares of Series B
Preferred Stock and Common Stock, respectively, holders of Series B Preferred
Stock and holders of shares of Common Stock shall receive their ratable and
proportionate share of the remaining assets to be distributed in the ratio, on a
per share basis, of the Adjustment Number to 1 with respect to such Preferred
Stock and Common Stock, on a per share basis, respectively.

     (A) In the event, however, that there are not sufficient assets available
to permit payment in full of the Series B Liquidation Preference and the
liquidation preferences of all other series of Preferred Stock, if any, which
rank on a parity with the Series B Preferred Stock, then such remaining assets
shall be distributed ratably to the holders of such parity shares in proportion
to their respective liquidation preferences.

     (B) In the event the Corporation shall at any time following May 31, 1996
(i) declare any dividend on Common Stock payable in shares of Common Stock,
(ii) subdivide the outstanding shares of Common Stock or (iii) combine the
outstanding Common Stock into a smaller number of shares, then in each such
case the Adjustment Number in effect immediately prior to such event shall be
adjusted by multiplying such Adjustment Number by a fraction the numerator of
which is the number of shares of Common Stock outstanding immediately after
such event and the denominator of which is the number of shares of Common Stock
that were outstanding immediately prior to such event.

S7. Consolidation, Merger, etc.  In case the Corporation shall enter into any
consolidation, merger, combination or other transaction in which the shares of
Common Stock are exchanged for or changed into other stock or securities, cash
and/or any other property, then in any such case the shares of Series B
Preferred Stock shall at the same time be similarly exchanged or changed in an
amount per share (subject to the provision for adjustment hereinafter set forth)
equal to 100 times the aggregate amount of stock, securities, cash and/or any
other property (payable in kind), as the case may be, into which or for which
each share of Common Stock is changed or exchanged.  In the event the
Corporation shall at any time (i) declare any dividend on Common Stock payable
in shares of Common Stock, (ii) subdivide the outstanding Common Stock or (iii)
combine the outstanding Common Stock into a smaller number of shares, then in
each such case the amount set forth in the preceding sentence with respect to
the exchange or change of shares of Series B Preferred Stock shall be adjusted
by multiplying such amount by a fraction the numerator of which is the number of
shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

S8. Redemption.  The shares of a Series B Preferred Stock shall not be
redeemable by the Corporation.  The preceding sentence shall not limit the
ability of the Corporation to purchase or otherwise deal in such shares of stock
to the extent permitted by law.

S9. Ranking.  The Series B Preferred Stock shall rank junior to all other series
of the Corporation's preferred stock (whether with or without par value) as to
the payment of dividends and the distribution of assets, unless the terms of any
such series shall provide otherwise.

                                     -6-


<PAGE>   17


S10. Amendment.  The Certificate of Incorporation of the Corporation shall not
be amended in any manner which would materially alter or change the powers,
preferences or special rights of the Series B Preferred Stock so as to affect
them adversely without the affirmative vote of the holders of a majority or
more of the outstanding shares of Series B Preferred Stock, voting separately
as a class.

S11. Fractional Shares.  Series B Preferred Stock may be issued in fractions of
a share which shall entitle the holder, in proportion to such holder's
fractional shares, to exercise voting rights, receive dividends, participate in
distributions and to have the benefit of all other rights of holders of Series
B Preferred Stock.

     IN WITNESS WHEREOF, U.S. Robotics Corporation has caused its corporate
seal to be hereunto affixed and this Certificate to be signed by Casey Cowell,
its Chairman, President and Chief Executive Officer, and the same to be
attested by George A. Vinyard, its Secretary, this 9th day of May, 1996.


                                           U.S. ROBOTICS CORPORATION



                                           By:    /s/ Casey Cowell
                                              -------------------------
                                                Casey Cowell
                                                Chairman, President and
                                                Chief Executive Officer



(SEAL)


Attest:


By:  /s/ George A. Vinyard
     ---------------------
     George A. Vinyard
     Secretary


                                     -7-