pdp11/84 PMI memory: What is the problem with Q bus?

Chris Zach cz at alembic.crystel.com
Thu Apr 23 19:51:14 CDT 2020

Oh I'm using an MTI MQD13 card as my disk controller. It is a MCSP 
controller that can interface up to 4 ESDI drives to Q Bus. Pretty fast.

Just checked the configuration and block mode DMA *is* off. Wonder what 
happens if I turn it on...

It does have a lot of knobs to fiddle with, so maybe I can figure out 
what works and what does not for these memory boards. Experimentation!


   DMA CHARACTERISTICS:                         DRIVE 2... ESDI
         BLOCKMODE............ OFF                FIRST LOGICAL...... 002
         BURST LENGTH (WORDS).  16                SECOND LOGICAL..... 006
         THROTTLE............. ON                 DRIVE 3... ESDI
         DWELL us.............  1.6               FIRST LOGICAL...... 003
                                                  SECOND LOGICAL..... 007
     SEEK MODE................ OVERLAPPED
         SEEK OPTIMIZATION.... ELEVATOR       COMMAND QUEUE.......... 008
         FAIRNESS VALUE....... 016

On 4/23/2020 1:17 AM, Mark Matlock via cctech wrote:
>> Date: Tue, 21 Apr 2020 16:17:07 -0400
>> From: Chris Zach<cz at alembic.crystel.com>
>> To:cctalk at classiccmp.org
>> Subject: Re: pdp11/84 PMI memory: What is the problem with Q bus?
>> Message-ID:<27647f0e-19d4-b484-d288-e9f3bb715363 at alembic.crystel.com>
>> Content-Type: text/plain; charset=utf-8; format=flowed
>> Thanks Mark! Actually this was just the boards from the 11/84 (no idea
>> what happened to the chassis, drat) so it's an 11/84 CPU (18mhz, FPP
>> chip installed), 2 PMI boards (one old 2mb, one new 1mb) a console board
>> of some sort and the Unibus map.
>> I popped this into my BA23 to speed things up a bit in place of my quad
>> height 11/73 CPU with 2mb memory. So far it seems to work, and with the
>> CA memory in the PMI slot managed to boot RSX11M 4.2 and compile up EMPIRE.
> Chris,
>     I understand now. I also have a PDP-11/83 in a BA123 box and the CPU and
> PMI memory (M8637-E) can move from the Qbus box to the 11/84 box and work fine
> In either. I spent a good bit of time tinkering with the 11/84 power supply which did not
> Work until I put a M7556 minimum load module in it. Basically the ± 12 Volts needs a
> Load or you get a hung bus error. Also, with the Unibus you have to pay attention to
> The NPR/NPG grant jumpers.
>     For disks on the QBus systems I used the UC07 and SCSI2SD. The UC07 can be
>   can be configured for block mode transfers and I think it is doing it. I guess I’d need
>   to hook up a logic analyzer to know for sure.
>      The 11/84 uses a UniBone and when it is emulating a MSCP disk, it can do 150
> I/Os a second (using IOX on RSX11M+) The 11/83 using the UC07 and a SCSI2SD
> Does about 60 I/Os per second. I think the UC07 could go faster but is limited by the
> SDcard interface. I need to put a fast real SCSI disk on it sometime and see what it can do.

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