RT-11 doesn't recognize my 3.5" floppy

Charles charlesmorris800 at centurytel.net
Wed May 8 08:46:53 CDT 2019

On 05/07/2019 11:15 AM, Douglas Taylor via cctalk wrote:
> Very interesting , now that you got it to work, what can you use it for?
> Will it be an exchange media with PUTR?
> Doug
> On 5/6/2019 6:20 PM, Charles via cctalk wrote:
>> I have installed an RQDX3 and the M9058 distribution board in my
>> 11/23+. Since I don't have a 5.25" drive yet, I hooked up a 3.5" HD
>> (1.44 MB) drive from an old PC.
>> After a struggle (which I documented on VCFED's DEC forum), I managed
>> to get all the jumpers and cables set correctly, and now my XXDP
>> diagnostics (ZRQA?? ... ZRQF??) recognize the drive as an RX33 (DU0:,
>> logical drive 0 since no hard disks are attached). It passes all the
>> tests, and I can INIT, DIR, and copy files to it using the limited OS
>> with the XXDP suite. The LED on the RQDX3 blinks once when the drive
>> is accessed. So far so good.
Did you actually test the drive by formatting, reading and writing?

>> But, when I boot the system (with RT-11SJ V5.01), it can't see the
>> drive at all. Attempts to access it result in the command hanging
>> indefinitely, the drive does not select, and the RQDX3 lamp flashes
>> rapidly. SHOW DEV:DU does say that the handler is installed for the
>> correct 172150, 154 location. However, SHOW DEV:DUn where n=[0..3]
>> displays two blank lines then back to the dot prompt.
>> Is my version of RT-11 just too old to recognize an RX-33? If so,
>> what do I need to fix this? Presumably a later DU.SYS?
>> Thanks for any help. Most of my experience is with PDP-8's so this is
>> slow going...
>> -Charles

RT11V5 works for me using RQDX3 and the distribution board in the BA23
box assembled as a MicroPDP-11 with RX33
and RD52 (Quantum 31mb).  Never thought much about it other than to make
sure the RX33 was jumpers were correct
and making a dummy panel for the smaller than RX50 drive.

The 11/73 system has the RQDX3 and the signal distribution board (m8058)
out of BA123 to hook up
RD52, RX33, RX23 and never had issues due to addressing devices under RT11.

Is it possible you have a interrupt grant gap between the various boards
and the RQDX?  That would cause a hang.

If you successful it makes using PUTR easier though RX50 works for that
too just smaller.
Not a hardware or installation problem (once I got everything hooked up 
right, that is)...

As another member helpfully pointed out, 5.04 is the first version of RT11 
that supports RX33. I have 5.01 on my TSX+ RL02 pack.
Once I booted with an RT11XM 5.04 disk, I can format, read and write the 
floppy :)

Now I have to figure out how to upgrade to RT11SJ 5.04 or later without 
bombing the contents of the RL02. Remaking a pack with VTserver is a pain.

Yes, the plan is to use PUTR on an old Windows box that I use with my PDP's.

I'll probably use Front Panel Express to make a nice rack panel for a 3.5" 
and a 5.25" drive, instead of having the bare drive sit on top of the RL02 
in the corporate cabinet ;)

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