Homebrew QBus designs - was Re: VAX 4000-100 QBUS cables

allison ajp166 at verizon.net
Wed Nov 30 06:22:37 CST 2016

On 11/29/16 1:24 PM, Charles Dickman wrote:
> On Tue, Nov 29, 2016 at 12:54 PM, Toby Thain <toby at telegraphics.com.au> wrote:
>> On 2016-11-29 12:22 PM, Noel Chiappa wrote:
>>>      > From: Peter Coghlan
>>>      > Can anyone suggest an existing, simple QBUS device that I could
>>> study
>>>      > the documentation of to figure out what a basic QBUS device needs to
>>>      > have and to give me some ideas on how to implement one?
>>> Depends. Do you want to be able to do interrupts? Do you want to be able
>>> to
>>> do DMA? Each is a significant increment in complexity.
>>> Later DEC QBUS devices may not be the best things to look at, since they
>>> tend
>>> to use special DEC QBUS control chips (I'm _not_ talking about bus
>>> transceiver chips here) which are of course no longer available.
> The DEC Chipkit documentation has the internal schematics for the
> standard DEC interface chips and is very much worth a read.
The major advantage of using chipkit parts is space.  If you build on a 
quad wide board
then its fairly easy to do DMA, bus arbitration, interrupt chain, and 
interrupt vectors
as its all documented in the various Qbus PDP-11 books.

About the only thing I've done is simple parallel interfaces as any 
other function
was available built.  Though one of these days a CF  "disk" board with 
boot rom
would be handy.  that would make a 11/23, dlv11j, memory and self contained
disk card a nice 4 board system in a BA11-VA box.


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