MEM11 Status Update

Henk Gooijen henk.gooijen at
Tue Jan 20 10:44:15 CST 2015

-----Oorspronkelijk bericht----- 
From: Guy Sotomayor
Sent: Tuesday, January 20, 2015 6:27 AM
To: cctalk at
Subject: MEM11 Status Update

As some of you know I've been working (on and off again) a
multi-function Unibus board that contains all of the more difficult
items to allow a PDP-11/20 to run Unix V1 entirely within the CPU
chassis.  Other than the CPU and the RK11-D controller, everything else
will be on the MEM11 board.  Here's the background on what the MEM11 is
and the current progress.

TTFN - Guy

Awesome Guy, excellent job! Looking forward to see some documentation.
Having read the responses, these are my thoughts.
Your current implemented device list is "good enough" for me, although
I can understand that people would like simulated RK05 drives. But I do
have an RK11 ... but RP11 will never be possible, isn't that MASSBUSS!?
A real RX01 is not too difficult to obtain and would go nice with the /20.
BTW, the RX01 emulator would also fit, giving you an emulated RX
floppy drive on a PC connected via the LPT: port ... I'm rambling ... ;-)

Ahhh, the "old story" of correct PDP-11 bus receivers/transceivers ... If 
install the MEM11 "option", how much additional bus loading will you ever
do? I can see an RK11 or RX11, but what else?  So, wouldn't it be possible
to use the TTL "replacements"?  IIRC 7439 or something with those numbers.

If I can afford the MEM11, I am in for one ... probably have to get my 11/20
CPU back in working order first though !

A stupid idea just came to me, forgive me.
If there is room left on the PCB, would it be possible to add two 8-bit 
One connects to address lines 0~7, and the other to 8~15. If you add an
old-style TEK scope (the one with the rectangular CRT in the middle and at
both sides one plug-in unit) and connect the DAC outputs to X and Y, you
can see "where in the memory" the CPU is fetching/storing data. I saw
that "screen output device" once on a picture :-)

Thanks for this great effort, looking forward to read/see more!
- Henk, PA8PDP

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