I think you can make use of those 2 bits by implementing double parity check!!!!! I mean you can check if bits 0,2,4,6,...... are changed with one parity bit,and check for the other bits 1,3,5,7...... with the other You can do this easily with what is known as Algebraic Coding. You can search for its details in a networking or communications book. Mohamed Eldesoky ^^^^^^^^^^^^^^^ Life is to try ^^^^^^^^^^^^^^^ ----- Original Message ----- From: "Automatic digest processor" To: "Recipients of PICLIST digests" Sent: Thursday, March 29, 2001 5:14 AM Subject: PICLIST Digest - 27 Mar 2001 to 28 Mar 2001 - Special issue (#2001-89) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics