On Thu, Mar 19, 2020 at 8:16 PM Paul Koning <paulkoning at comcast.net> wrote: > I thought 2780 uses BISYNC, which is a different protocol. X.25 is HDLC. Yes. You are correct. I used to make and sell COMBOARD 2780/3780, HASP and SNA communication boards for Qbus, Unibus and VAXBI. 2780/3780 is Bisync not HDLC. -ethan