> I'm working on the prints now. OK, done and uploaded:
http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/RK11-C-DB_EngrDrws_Dec72.pdf I haven't had the time to pore over them to figure out exactly what the changes do, but they add two buffer registers (ABUF and BBUF), so they probably offer greater resilience to DMA contention on the UNIBUS. I don't yet know if they are used for write as well as read (the RK11-C-DB block diagram in the prints suggests not, as it doesn't show a path from any RK registers to the ABUF, just from the UNIBUS - i.e. only usable on reads), or if there are any user-visible programming changes (I suspect not). For those with an RK11-C, these prints are somewhat clearer than the prints for the 'basic' RK11-C which are online, so although there are a number of changes (see: http://gunkies.org/wiki/RK11-C_disk_controller#Engineering_drawings for info on which sheets have changes), use of these can help decipher some of the hard-to-read pages of the 'basic' RK11-C drawings. Also, the prints for the 'basic' RK11-C are missing a couple of pages: 18 - Disk Cable and Termination 19 - Bus "D" Drvrs and Rcvrs which are present (albeit perhaps modified, for the second one) in this set. Noel
