General TC11 DECtape diagnostic/formatter questions

Josh Dersch derschjo at
Tue Nov 8 14:37:56 CST 2016

Hi all --

I'm working on getting a TC11 + TU56 running at the LCM+L.  We plan to use
it as a tool for various archival and restoration efforts.

After restoring the power supplies, I have it lashed up to a PDP-11/44 -- I
know this is anachronistic, but it's been a workhorse machine with ethernet
and SCSI, which makes it very flexible.  So far, so good.  I have RT-11
running and it can read and write tapes, although the left TU56 transport
seems to be a bit marginal.

I am running into a couple of issues, and I'm curious if anyone else out
there has experience here and might be able to shed some light before I
spend a lot of time on it:

1) In bringing the TC11 up, I've been attempting to run the TC11
diagnostics, with mixed success.  ZTCB runs, but reports an error with the
ENDZ status bit not being set properly.  So far as I can tell, ENDZ *is*
being set on normal operations, but I haven't exhaustively debugged the
controller yet.  The other four diagnostics (ZTCA, ZTCC, ZTCD, and ZTCE) do
nothing when run -- nothing is printed and there is no response.  If I run
them on SIMH configured as an 11/44, I see the same behavior.  If I run
them on SIMH configured as an 11/20, then I get the printout described in
the documentation and listings.  (See bitsavers --
I haven't yet dug in to see what accounts for the difference -- any ideas?

2) I'm looking for means to format DECtapes on the TC11.  I have a few
marginal tapes and I'd like to see if reformatting them brings them back to
life.  The maintenance manual only indicates "a special program supplied
with the TC11 system," and I haven't managed to find it. I *have* found
which I've assembled and run on RT-11 and it goes through the motions of
writing out the timing and mark tracks, but when it goes through the second
pass to write out the block numbers it fails immediately, with either
status 001207 (indicating a "Data Missed" error) or 020033 (Mark Track
Error).  I haven't yet hooked up a scope to see if the T&M tracks are
*actually* being written, but given my experience with the diagnostics in
(1) above, I'm not averse to thinking there may be more than meets the eye
with this issue.

So in a nutshell:  Anyone used a TC11 on a later PDP-11 (like the 11/44)?
Anyone have any thoughts on the diagnostics and formatter issues?

Thanks as always,

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