MFM or ESDI QBUS controller for one PDP-11/23 PLUS - test-drb@ccmp.vtda.org

9 Oct 2007

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Subject: Re: MFM or ESDI QBUS controller for one PDP-11/23 PLUS
   From: "Sergio Pedraja" <spedraja at gmail.com>
   Date: Tue, 09 Oct 2007 08:57:56 +0200
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

Hi, Allison.

I'm perplexed.  The RQDXn controllers are MFM and Floppy.  Best shot
  is late firmware RQDX3 as it does RX33 and most
all MFM drives.  Its
 also easier to find.

 At least as I can remember, the RQDx3 needs an internal distribution 
 panel. I'm searching for ONE single board. 
Understood.  Most of the nonDEC FM/EDSI boards still require a 
distribution pannel as they were targeting DEC systems.  At a minimum
you need to make a hybrid cable to use them with one drive. How can you
tell?  Simple, if the board is said to do FM/EDSI and has only a 50pin 
connector a breakout board (distribution pannel) is required.  Most do.

I have several differnt examples of nonDEC MSCP controllers
for floppy and hard disks and they all like the 50pin cable to 
breakout.  There may be some that do not I don't have one.

Actually there are several possible distribution or breakout 
boards.  They primarily serve to translate the 50pin RQDX cable
to the more typical cables used for floppy and FN/EDSI disks.

One is the distribution pannel used in the BA23 and its only 
connectors and wires so easily duplicated.  Its function is to 
take the 50pin cable from the RQDXn (or nonDEC MSCP) and route 
them to the 34pin connector for floppy and the 26/34 pin cables
used for MFM. It is located in back of the drive bay of the BA23
and can be used outside of BA23.

The second is the M9058 used in the BA123 and that is a dual width 
Qbus board that can support 1 floppy and 3 hard disks.  It's Qbus but
only takes power for running the local buffers and extended device 
select plus providing the interconnect point for the ready/writelock 
switch pannel. While it appears complex it's really trivial and is
better described as a breakout board. If You get a M9058 it is not
required to install it on the Qbus, only provide it with needed 
power if that is mechanically more suitable.  The reason for that
is while it's dual width it's thick due to the presence of many 
connectors. The M9058 is typically located outside the BA123
backplane cage nearest the disk bays for easy cable routing.

There is a third board RQDXE that is for use mostly in BA23s for
extending the RQDXn outside the case for additional drives. Its
of limited utility as breakout/distribution.

I know this from fitting two half height HD + RX33 in ba23 and also 
putting RQDX3 in BA11S with RX33 and 3 RD52s. 

Hope this helps.

The only MSCP boards I've used that didn't require breakout were
SCSI.

Allison