The error signal was wire-or'ed through up to four drives, so it must be
terminated somewhere - IIRC there was a Unibus terminator in the last
drive, but it has been 45 years since I worked on them, the little grey
cells are fading _\:-)
cheers, Nigel
Nigel Johnson, MSc., MIEEE, VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
Skype:  TILBURY2591 nw.johnson at 
ieee.org
On 09/07/2020 20:02, Robert Armstrong via cctech wrote:
  ? I have an 11/04 with an RK11-D.? I have a couple of
RK05s, but I
 wanted to test the controller before I start working on the drives.?
 The PDP11 Diagnostic Handbook says that ZRKJ?? "checks only the
 drive-independent logic of the RK11 controller. no drive is
 needed..."? I assumed that meant it was a diskless test, but now I'm
 not sure that's true.? Can anyone confirm or deny this? Does anyone
 have a listing of ZRKJE0?
 ? My RK11-D has the BC11 drive cable plugged into the backplane, but
 the free end of the cable is just lying on the floor.? No drive is
 connected.? The test fails with
 ??? RK11 LOGIC TEST I
 ??? MAINDEC-11-DZRKJ-E
 ??? REGISTER NOT CLEARED
 ??? ? PC?? REGADD??? RECVD
 ??? 002560? 177402? 100000
 ?177402 is the RKER register and bit 15 is DRE - "Drive Error".
 According to the manual this bit is set when the AC power to the drive
 is lost, which given that I don't have a drive at all, doesn't sound
 unreasonable.? Continuing ZRKJ?? also gives
 ??? REGISTER NOT CLEARED
 ??? ? PC?? REGADD??? RECVD
 ??? 002560? 177404? 140200
 ??? RKCS ERROR
 ??? ? PC??? WROTE?? READ
 ??? 002636? 000002? 140202
 177404 is the RKCS register and the first two bits are ERROR and HARD
 ERROR.? These are both set by the DRE bit in RKER and aren't really a
 surprise.
 ? I'm starting to wonder if this diagnostic really works w/o a drive
 attached, or if these errors are expected.
 Thanks,
 Bob