yet another pdp-11 in fgpa

RodSmallwood rodsmallwood at
Wed Jun 30 00:08:17 CDT 2010

Thanks for the concise reply. 
Speed is not an issue. J11 speed would be just fine.


-----Original Message-----
From: cctech-bounces at [mailto:cctech-bounces at]
On Behalf Of Walter F.J. Mueller
Sent: 26 June 2010 21:24
To: cctech at
Subject: RE: yet another pdp-11 in fgpa

RodSmallwood" <rodsmallwood at>  wrote:
 > How difficult would it be to extend one of these FGPA PDP-11's to be put
 > on a quad DEC board and be a plug in replacement for say an 11/93 or
 > 11/94 CPU. (M8981-AA OR 11/91-BA)?
 > Rod

Hi Rod,

possible and feasible, but requires three tasks to be addressed:

1. an adapter board is needed to connect the FPGA development
    boards (holding the FPGA and memory) to the UNIBUS or QBUS.
    Main active part of this adapter board are the bus transceiver
    for UNIBUS or QBUS.
2. The UNIBUS or QBUS bus interface logic can be added to the
    FPGA. Given that the system clock period is small compared
    to typical times of these buses it is quite simple and
    straight forward to implement such a bus interface.
3. the current w11a implementation doesn't support bus masters
    on the I/O bus. DMA transfers from disk/tape devices are
    currently emulated. Next versions of the FPGA implementation
    however will add this functionality.

But keep in mind: the current FPGA implementation isn't tremendously
faster than a J11.


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