Double Buffer RK11-C

[Noel Chiappa]

    > 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