3 Jun
2011
3 Jun
'11
7:07 a.m.
Tim Thompson wrote:
I've run BA23's with either an RX50 or TK50,
and a pair of piggy-backed RD32's. It seemed to work well.
It is also possible to place the hard disk drives outside
the BA23 and use longer cables than normal to connect
the drives to the normal distribution points inside the
BA23 box. This frees up the 2 drive bays for the RX50
and the TK50 or a TK70. In general, I have found that
RT-11 works very well with a TK70 when I use a PDP-11/73
or faster CPU. I recently attempted to use the TK70 with
a PDP-11/23 and found that writing to the TK70 was not
reliable.
I also STRONGLY recommend that when 2 hard disk
drives, an RX50 and a TK50 are all used on a BA23
box, an additional PC power supply be used just for
the 2 hard disk drives. Otherwise, there will probably
be too much current required on the 12 volt supply.
In addition, the TK50 requires the power directly
from the BA23 (at least in my experience).
I had soldered a pair of 2.2K (?) resistors
onto the back of the 4-button panel to force the 2nd drive
"ready" and "write enabled" full-time.
I may have the details on that particular modification
tucked away in my documentation somewhere.
I will note my simple extra circuit. I inserted a
10" temporary 10 pin cable into the standard
circuit (to the front panel of the BA23) with
a female header at one end and the male header
at the other end so that the change was VERY
temporary. Within the extra piece of cable, I
soldered line 5 to line 1, line 6 to line 2 leaving
the portion leading the the front panel on the
BA23 hanging (unattached to anything). If I
remember correctly, grounding line 5 and line 6
did the same, but after more than 10 years, I
am probably wrong and the guess is only that!!
The net result is the both hard drives are serviced
but the single pair of buttons on the front panel so
that both drives are always in the same state. One
difficulty is to change the state of the READ ONLY
button. Under RT-11, it is sometimes necessary to
first UNLOAD DU:, then LOAD DU: which means
that DU(X).SYS can't be the Resident System
Device. In that case, I transfer the monitor files
and other few utilities to the VM: device.
I also worked up instructions a while back to
construct
a ribbon cable to go from an RQDXn controller directly to
an RX50 or RX33.
I should be able to dig that up as well, if anyone is interested.
Yes! Although I doubt that I would ever need to
use that circuit. I rarely use the DEC hardware
these days as I run RT-11 under Ersatz-11 most
of the time.
By the way, I also have a dual RX33 configuration
that is held inside an empty (discarded) RX50 shell
that was from a bad RX50 drive. The RX50 shell
makes the two RX33 drives look just like an RX50
at first glance, but the lever to use the diskette gives
the situation away at a closer inspection Of course,
the RX33 requires an RQDX3 controller. But RT-11
itself (first time ever that DEC supported this function
directly within RT-11 for a floppy diskette media) is
also able to perform a LLF (Low Level Format) on
the RX33 media which is identical to the HD 1.2 MB
5 1/4" PC media and can be formatted on the PC as
well if not already formatted (i.e. LLF) when purchased.
Jerome Fine