[CCTECH]PDP11/23 and Emulex Qbus Controller

From: Andreas Freiherr <Andreas.Freiherr_at_Vishay.com>
Date: Mon Jul 15 13:08:00 2002


maybe someone else will provide practical experience with the
combination QD32 & 11/23, but my first guess would be that bandwidth is
not a problem: as long as all devices on the bus obey all the bus
specifications, they should be compatible.

Was your friend possibly talking about address width (in other words,
the number of address lines on the bus)? - There are three variants,
with 16, 18, or 22 address lines. Incompatibilities can arise if a *DMA
controller* drives *less* address bits than the system actually uses.
Non-DMA controllers have no problem because they never address memory
themselves. A typical problem of this type is the RXV211 (RX02 floppy
disk controller: DMA, 18 address bits) used in a 22 bit system. The
problem can be circumvented in driver software by reserving a buffer
area in the lower 256kB of main memory.

IIRC, older versions of the 11/23 drive 18 address lines, making them
capable of using up to 256kB (or 128kW) of memory. Later models (in
particular, the 11/23-PLUS) supply all 22 possible address lines,
allowing for up to 4MB (2MW) of RAM. I was told several years ago that
some /23s can be upgraded by adding a couple of wires (and maybe a
handful of bus drivers).

The QD32 is no doubt a DMA controller, but I think I know it is 22 bit.
Hence, it should be possible to use this controller in any Qbus system.

Also IIRC, the QD32 uses MSCP to communicate with its driver software,
so it should not even require any special software: a vanilla DU driver
would be OK for RT-11 or RSX-11, for example.

Anyone have better information to correct me?


P.Gebhardt_at_gmx.de wrote:

> Hello,
> is it possible to use an EMulex QD32 Controller (Qbus) with a PDP11/23 ?
> I asked a friend and he told me that the bandwith of the bus could be
> drifferent.
> Is it right ?
> Greetings
> Pierre

Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
cctech mailing list
Received on Mon Jul 15 2002 - 13:08:00 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:35:01 BST