I found that it helps to search for WD179x or WD279x when looking for Western Digital FDC data sheets. A good set of WD179x (and WD1771) data sheets and appnotes can be found on David Keil TRS-80 page. http://discover-net.net/~dmkeil/trspdf.htm On the tool bar on the left side go down to the "TRS-80 Books & Technical Manuals" icon. A copy of the 279x data sheeets can be found on my site. http://www.swtpc.com/mholley/DC_5/TMS279X_DataSheet.pdf Michael Holley