below On Wed, May 1, 2013 at 3:20 PM, Mark Pizzolato - Info Comm <Mark at infocomm.com> wrote: I would work with the DZ device first. It has been tested and had its modem related behaviors more solidly verified. This line had me chuckling. DZ were notorious for being lousy at supporting modems because they lacked all a number of the needed RS-232 modem control lines. Its one of the many reasons why the UNIX community in those days, used to recommend using Able Computer's DH/DM solution. Which was 16 serial lines with full modem control on a single unibus board (and as described previously used DMA and had character buffering), The Able DH's actually could run at faster speeds than the DEC one did.