EXHIBIT 5.1




         Woodbridge

___________________, 1999


NETsilicon, Inc.
411 Waverly Oaks Road
Suite 227
Waltham, MA 02154

         Re: NETsilicon, Inc.

Ladies and Gentlemen:

         We have acted as counsel to NETsilicon, Inc., a Massachusetts
corporation (the "Company"), in connection with its filing of that certain
Registration Statement on Form S-1, as amended (Registration No.333-62231) with
respect to an aggregate of 3,000,000 shares (the "Offering Shares") of
common stock, $.01 par value of the Company (the "Common Stock") to be issued
and sold by the Company and Osicom Technologies, Inc. (the "Selling
Stockholder") to a group of underwriters (the "Underwriters") represented by
Dain Rauscher Wessels, of which 2,000,000 shares of the Common Stock are
being issued and sold by the Company and 1,000,000 shares of the Common Stock
are being issued and sold by the Selling Stockholder. In addition, the
Underwriters have been granted options by the Selling Stockholder to purchase
up to an additional 450,000 shares of the Common Stock (the "Over-Allotment
Shares"), for the purpose of covering over-allotments in connection with the
sale of the Offering Shares. The Offering Shares and the Over-Allotment Shares
are hereinafter collectively referred to as the "Shares".

         As counsel to the Company, we have examined the Articles of
Organization and By-Laws, as amended to date, and other corporate records of the
Company and have made such other investigations as we have deemed necessary in
connection with the opinion hereinafter set forth. We have relied, to the extent
we deem such reliance proper, upon certain factual representations














NETsilicon, Inc.
_________, 1999
Page 2

of officers and directors of the Company given in certificates, in answer to our
written inquiries and otherwise, and, although we have not independently
verified all the facts contained therein, nothing has come to our attention that
would cause us to believe that any of the statements contained therein are
untrue or misleading.

         In making the aforesaid examinations, we have assumed the genuineness
of all signatures and the conformity to original documents of all copies
furnished to us.

         Based solely upon and subject to the foregoing, we are of the opinion
that the Shares have been duly and validly authorized and, when issued and paid
for, will be duly and validly issued, fully paid, and non-assessable.

         We hereby consent to the filing of this opinion as an exhibit to the
aforesaid Registration Statement, as amended and to the reference to our firm
under the caption "Legal Matters" in the Prospectus constituting a part of said
Registration Statement, as amended.

                                Very truly yours,



                                GREENBAUM, ROWE, SMITH, RAVIN,
                                     DAVIS & HIMMEL LLP