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My first Omnibus interface - Progress so far

intabits

Experienced Member
Joined
Jan 22, 2019
Messages
145
Location
Melbourne, Australia
This is my first Omnibus interface card, using the flip-chip adapter boards shown in this thread:-

https://www.vcfed.org/forum/forum/g...l-purpose-flip-chip-adapter-board-worth-doing

It's a mash-up of the boot-loader designs by Malcolm Macleod and Roland Huisman, plus some extra stuff:-
* power supply voltage monitoring,
* ability to read the memory address and memory data buses

Links to projects by Malcolm & Roland:-
https://avitech.com.au/?page_id=3372
https://github.com/Roland-Huisman/M847-extended-version-V1.1
https://www.youtube.com/watch?v=0nqb3zyAv2g&ab_channel=proxxima038

OBI-F.jpg

OBI-B.jpg

-----------

As I expected, the many wire links were a problem because the 0.8mm holes are a bit too large for the size of the via pads. There were about 6 or 7 bad solder joints, and I had to fix each of them as I encountered the problems they caused. The pdp8/f would not even tolerate the board being installed until I fixed the first 3 or 4. After that, it would at least operate with the board installed.

Then came a few days of understanding how the Omnibus signals needed to be manipulated in order to read and write memory, and to start and stop programs running. Roland and Malcolm's code was a big help here, but I struggled with this for a few days, until I found myself needing to control some signals in completely the *opposite* way to how Roland's code did it. And that's despite using exactly the same circuitry between the Nano and the Omnibus! This was for the INITIALIZE-H and PULSE-LA-H signals with type 5 loads, and needing type 10 transistor drivers.

Anyway, once the essential basics were sorted out, I could start making a PC based "control centre" program to make displaying and modifying memory possible, and providing a simple way to download programs to the PDP, and run them. The video below is a quick and rough description of where I'm up to with that.

This screenshot shows the program download page. A simple text file contains all the sample programs, which are listed at the left. The selected one is displayed on the right, and can be downloaded, and optionally run.

OBCC-1.png


This screenshot is of the memory display page, which shows a 4K field all at once, with facilities to fill areas of memory with specific values.

OBCC-2.png

Still to come is a memory test page that can download all sorts of data to memory, including random patterns, and check that they all read back correctly.

Video:-
https://youtu.be/O4OxPVE5jGM

I downloaded and ran programs on the PDP-8, and the only key on it's front panel that I touched was the power turnkey!
 

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Mike_Z

Veteran Member
Joined
Dec 1, 2013
Messages
1,620
Location
Near Milwaukee Wisconsin
Very nice indeed. I've been studying Python for the Arduino and Raspberry PI, but have not progressed to your level. Seems that technology is racing along faster than I can learn it. Sometimes I feel like I'm driving a tricycle in the Indy 500. Certainly looking forward to more on this. Thanks, Mike
 

intabits

Experienced Member
Joined
Jan 22, 2019
Messages
145
Location
Melbourne, Australia
Quite nice! Look forward to seeing the internals of your monitor program.
Very nice indeed. ... Certainly looking forward to more on this.

Thanks for the kind words!

At the moment, the code at both ends is all over the place like a dog's breakfast.
I'm still trying to nail down the communications operation and protocol, but just now starting to get some joy.
When it's sorted and cleaned up, I'll pack it all up for you to checkout. Might take a week or so...

Cheers,
Rob
 

intabits

Experienced Member
Joined
Jan 22, 2019
Messages
145
Location
Melbourne, Australia
I've done a bit more on this, but want to take a break and play with other toys, so for anyone interested, this is the project so far.

Schematic, PCB files, firmware, software is in the attached zip.

This is NOT a finished & polished project. The documentation above is for interest only.
But it may serve as a starting point for other projects, use it as you wish...

A quick update video:-
 

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