This blog is about youngsters finding an old Data General Nova 2 minicomputer, getting it to run, restoring it, learning all about it and having fun with all the stuff that goes along with it.

  • Taking Inventory

    So the other day I was over at the storage site where we keep the old Nova 2 to check out in detail what we got in terms of hardware in the computer and maybe establish a serial Connection.

    For making the serial connection I prepared an old Amstrad ALT-386SX portable computer my dad had still laying around. I figured the serial connection on that thing might be more compatible to old things than modern serial chips that mostly are just used with TTL voltages. I installed a copy of Kermit by the University of Columbia since it supports already a tonne of protocols and is able to emulate a very wide range of terminals, including a couple from Data General.

    Here is a photo of the test setup in my basement – Connection established!

    After several attempts to figure out where the serial connection of the Nova 2 is, we found an important clue in the manual:

    The connector is in the middle of the backplane, hidden amongst a vast amount of pin headers.
    And here is even a discription of what these pins do.

    Now unfortunately we found out, that the pin assignments point us to something called a current loop serial connection. And since the contemporal terminals we got with this machine are not (YET) working. We are now unable to connect them to our software emulated terminal, due to a lack of hardware compatibility.

    A next hint was a sticker on the basic IO board that says TTY 20mA. This means, that the serial connection does not require the usual TX, RX and Ground pins, but a VccTX, TX, VccRX and RX pin. A common ground is not necessary in this scenario, since the bits are not determined by voltage level like in a RS232 connection, but rather than by the flow of 20mA of electrical current.

    So since this was quite a show stopper for the day, I decided to order a Wieseman und Theis current loop adapter for 30 bucks on ebay, since 20mA current loops seemed to be quite common in industry for machinery and automation, so these things can be found quite cheaply. While waiting for this to arrive, we showcase below an inventory of the boards in the computer with a short description of what they (supposedly) do:

    And now as a special treat, we carefully took the time to open one of the core memory modules, to show you the beautiful art and great craftsmanship that went into these things.

    If I’m correct, this thing is able to store 4000 words of data, in this computer since it is a 16-Bit system, this would mean 64000 bits of memory, or 8 kilobytes per core memory module (we have two).

  • That Ominous Keyboard

    Starting the project, I picked the supposedly easiest piece of hardware out ot the bunch: The Keyboard!

    It was in a very sorry state, at least by the looks of it. Unfortunately I don’t have a picture of it in that state but it was really dirty and crusty. I took it home to disassemble it and give it a good clean as well. I took a picture of the keyboard layout, disassembled everything, pulled the keycaps and washed every single one individually with a brush, some soda and windex. Afterwards I let everything dry and removed all the dust and dirt from the pcb, the keyswitches, vacuumed the case and so on. The pcb was, apart from the dirt in a very healthy state. no corosion or broken tracks. Even the lacquer was not crumbling on the traces. I remember C64s that looked like a plowed field in atumn.

    Then it was puzzle time and at first I tried to put the keys back from memory but that didn’t take me very far. That was probably because the layout is a bit different from modern keyboards. Also notice the unmarked keys on the top. I wonder what they were used for. Maybe they are user programmable. According to the datasheet, at least the keyboard of the newer D100 Terminal has a ASCII code assigned to every key it seems.

    Also one of the turqoise keycaps had a broken alignment shaft. Fortunately some CA-glue made quick work of it and now it works reliable.

    Here are some shots of the stripped keyboard before and after cleaning:

    A few things I noticed along the way:
    The keyboard connector indicates to me, that it does not belong to the Dasher D100 terminal I got with the computer. According to some documents I found on the web, it should be an older model. This one features a 15 pin AMP connector, whereas the terminal just has a 9-Pin 2.54mm pitch single-in-ine dupont connector on it as depicted in the manual here: