PDP-11 compatible motherboard in mini-ITX form factor

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Buy black KR1801VM2 (КР1801ВМ2) on eBay and follow me ;)

At present PDP-11 computer systems are mostly forgotten, but there are PDP-11 compatible Soviet microprocessors still available on eBay (never used "old new" inventory) as KR1801VM2 (КР1801ВМ2 in Russian) and I'm going to bring PDP-11 back - I design an open source motherboard in mini-ITX form factor (170*170mm) around that chip with open source modules (see GitHub) that could fit into regular mini-ITX computer case (that is cheap) to make a true 16-bit modern retro computer with PS/2 keyboard (and may be mouse) connected to [S]VGA monitor:

As you can see design is inspired by famous RC2014 ;)

Mini-ITX spec with all sizes could be found here

I didn't want to use Q-bus as is (in it's original edge-connector form) because it's huge and almost half of contacts are not used, so I put all meaningful signals of Q-bus in 1-row header (slightly re-arranged) and in the same row (after 1 missed pin) I added all other signals from VM2 microprocessor and also de-multiplexed and inverted address lines (there are no modern ICs that could decode multiplexed Q-bus with proper handshaking natively so it will help to connect regular memory RAM and ROM chips) - so it's 62-pin header (37th pin is missing) that could fit in 6.3 inches ( 160mm that is coincidentally a limit for Eagle v5 Standard Edition that I own since 2007 ; ) and collectively I call this interface "Bread-Board friendly Q-bus extended" or BBQ-bus+ :)

PositionName (bold if Q-bus)
Where connected
1GNDGround - pin 1 and 20 of VM2
2BDMR L/DMR - pin 12 of VM2
3BSACK L/SACK - pin 13 of VM2
4BDMGI LDaisy chained BDMGO
BDMGO L /DMGO - pin 14 of VM2
6BHALT L/HALT - pin 29 of VM2
7BDCOK H/DCLO - pin 26 of VM2
8BPOK H/ACLO - pin 25 of VM2
9BINIT L/INIT - pin 27 of VM2
10BEVENT L/EVNT - pin 30 of VM2
11BIRQ4 L/VIRQ - pin 28 of VM2
12BIAKI LDaisy chained BIAKO
/IAKO - pin 24 of VM2
14BDIN L/DIN - pin 22 of VM2
15BDOUT L/DOUT - pin 18 of VM2
16BRPLY L/RPLY - pin 17 of VM2
17BSYNC L/SYNC - pin 21 of VM2
18BWTBT L/WTBT - pin 19 of VM2
19BBS7 LLogical 0 if A15=A14=A13=1
20BDAL0 L/AD0 - pin 9 of VM2
21BDAL1 L/AD1 - pin 8 of VM2
22BDAL2 L/AD2 - pin 7 of VM2
23BDAL3 L/AD3 - pin 6 of VM2
24BDAL4 L/AD4 - pin 5 of VM2
25BDAL5 L/AD5 - pin 4 of VM2
26BDAL6 L/AD6 - pin 3 of VM2
27BDAL7 L/AD7 - pin 2 of VM2
28BDAL8 L/AD8 - pin 39 of VM2
29BDAL9 L/AD9 - pin 38 of VM2
30BDAL10 L/AD10 - pin 37 of VM2
31BDAL11 L/AD11 - pin 36 of VM2
32BDAL12 L/AD12 - pin 35 of VM2
33BDAL13 L/AD13 - pin 34 of VM2
34BDAL14 L/AD14 - pin 33 of VM2
35BDAL15 L/AD15 - pin 32 of VM2
36PWR5V+5V (switchable) - pin 40 of VM2
38CLCICLCI - pin 16 of VM2
39CLCOCLCO - pin 15 of VM2
40A0Latched inverted /AD0
41A1Latched inverted /AD1
42A2Latched inverted /AD2
43A3Latched inverted /AD3
44A4Latched inverted /AD4
45A5Latched inverted /AD5
46A6Latched inverted /AD6
47A7Latched inverted /AD7
48A8Latched inverted /AD8
49A9Latched inverted /AD9
50A10Latched inverted /AD10
51A11Latched inverted /AD11
52A12Latched inverted /AD12
53A13Latched inverted /AD13
54A14Latched inverted /AD14
55A15Latched inverted /AD15
56A16/SEL - pin 31 of VM2 (virtual A16)
57SPARE1/WRQ - pin 10 of VM2 (pulled up)
58SPARE2/WAKI - pin 11 of VM2 (grounded)
59SPARE3/AR - pin 23 (wired to /SYNC)
62SPARE6Main +5V (permanent)


Open hardware license CERN OHL v1.2

Adobe Portable Document Format - 95.73 kB - 04/17/2018 at 08:14



    SHAOS03/09/2018 at 06:16 0 comments

    I just registered domain name ;)

    Now I'm thinking about a family of modules (main processor one and many peripherals) that shares the same bus ( breadboard friendly Q-bus extended or BBFQ-bus+ ; ) - all open source of course :)

    Using such modules anybody should be able to build "oversimplified" PDP-11 compatible machine or PDPii...

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Modzer0 wrote 3 days ago point

The J-11 is hard to find at a reasonable price. The Russian chips work but be sure to leave space for a heatsink as they get rather hot. I have the datasheets on those if you need them, in Russian, but the pinouts can be identified.

  Are you sure? yes | no

SHAOS wrote 3 days ago point

Thank you, but I have all information already and I can read Russian ;)
I even tried successfully run black 1801VM2s manually (step by step) - I'll soon document my experiments here...

  Are you sure? yes | no

Modzer0 wrote 2 days ago point

I'm working on learning more Russian. I am a fan of old computer systems. The older Russian designs is something I haven't had the opportunity to examine in depth. The PDP-8 and PDP-11 are two of my favorite architectures, and I know there were clones produced. I've restored systems and built replacement boards using FPGAs to repair and make spare parts for a couple of old systems that are still running RT-11 on a contract. I unfortunately can't share those as the client owns the designs and IP. I also don't want to make them angry as I had a lot of fun working with them. When you get your backplane specifications finished I look forward to designing some boards for it if I manage to find some free time.

  Are you sure? yes | no

SHAOS wrote 2 days ago point

Great, I'll probably will need your advice in very near future, because I'm familiar with PDP-11 instruction set only in scope of Russian machines build around PDP-11 compatible processors like Elektronika MK-85 (I own this one since 1991), Elektronika BK-0011M (recently bought one on eBay) and DVK-2 (first computer that I actually used in 1990 to learn coding in high school) and those machines were NOT clones of PDP-11 machines (no RT-11 or something was running on them). Total clones of PDP-11 line sure existed in Russia too (like Elektronika 60 and 100), but I never saw them and not even knew that they existed until like a few years ago...

P.S. Actually nobody told us in that time that 1801-series of microprocessors was PDP-11 compatible - I found out about that much later on Internet :)

  Are you sure? yes | no

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