This excerpt taken from the EXAS 10-Q filed May 6, 2005.
Article 6 - Exercise of Option.
Each eligible employee who continues to be a participant in the Plan on the last day of a Payment Period shall be deemed to have exercised his or her option on such date and shall be deemed to have purchased from the Company such number of full shares of Common Stock reserved for the purpose of the Plan as the participants accumulated payroll deductions on such date will pay for at the Option Price, subject to the maximum share limit of the option and the Section 423(b)(8) limitation described in Article 5. If the individual is not a participant on the last day of a Payment Period, the he or she shall not be entitled to exercise his or her option. Only full shares of Common Stock may be purchased under the Plan. Unused payroll deductions remaining in a participants account at the end of a Payment Period by reason of the inability to purchase a fractional share shall be carried forward to the next Payment Period.