On 2013-01-06 21:47, John Wilson wrote: I still can't find where it says "8085A" in the 110/130 manual, but page B-3 gives I/O page timings and mentions an "I/O microprocessor" and the fact that word I/O takes 90 usec but byte I/O takes 180 usec. So that certainly explains the difference in the DUV driver. Plus the manual specifically says that RSX11S is available for the /110, so I guess it was even supported! Sweet. Also mentioned on page 4-6, but pretty much with the same level of detail. Byte writes cause a read-modify-write. Time of 180 usec. And there is an (unmentioned) 8-bit microprocessor acting in between the PDP-11 and any peripherials. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol