Superboard /// Port of JMON

JMON is a machine language monitor program I wrote for the Briel Replica 1, a replica of the Apple 1. It was only natural to want to port it to run on my new Superboard ///. Given that both computers use a 6502 microprocessor, and JMON has minimal hardware dependencies, it was not hard to do. In one evening I had it all working on the Superboard ///.

After determining the addresses of suitable keyboard input and screen output routines, I very quickly got it up and running. Most of the work to fully port it was to adapt the output to the smaller screen width (24 characters) of the Superboard. I also had to disable some features that did not apply. It is now fully working and is quite useful, particularly as the built-in OSI machine language monitor is very primitive.

Years ago, when I had an original Superboard II, I wrote some machine language programs by hand assembling them and entering the hex codes into the monitor. I very quickly wrote a disassembler in BASIC in order to help verify and debug my programs.

JMON is cross-compiled on a desktop computer, and both the Apple Replica 1 and Superboard /// versions build from the same source code using ifdefs for conditional code.

Below are some representative screens showing some of the commands.

Initial Screen

Help command

Disassemble command

Memory Dump command

Info command

Changing registers and single stepping

Memory test

The Superboard ///

My latest retrocomputing project is building the Superboard /// computer kit by Briel Computers.

It is a replica of the Ohio Scientific Superboard II. The original SuperBoard II was one of the first affordable computers that featured a full keyboard, video output, BASIC in ROM.

At a price of $279 in 1979, it was an amazing bargain at the time when compared to systems like the Apple II that retailed for about $1300. For that you got an assembled board but needed to add a 5 volt power supply, monitor or TV set and RF modulator, and cassette tape for storage.

I owned one that I purchased in 1979 and it was my first computer. With it, I learned BASIC and 6502 machine language programming.

The SuperBoard /// is Vince Briel's replica of the original SuperBoard. It features a 6502 processor, but simplifies the design by replacing a lot of logic chips with a Propeller CPU. It is software compatible with the original system.

It is sold assembled or as a kit. I opted for the kit.

To date I've made three YoutYube videos on the kit, covering unboxing, assembly, and basic operation. They can be found on my YouTube channel.

I also have some files on my github account including a handy Quick reference, the OSI firmware including BASIC, and a port of my JMON monitor program. The Visual Monitor program that I entered a few months ago also works.

Below are some useful web links.

My Stuff:

• https://www.youtube.com/user/jefftranter
• https://github.com/jefftranter/6502/tree/master/asm/BeyondGames
• https://github.com/jefftranter/6502/tree/master/asm/OSI
• https://github.com/jefftranter/6502/tree/master/asm/docs
• https://github.com/jefftranter/6502/tree/master/asm/jmon

Ohio Scientific:

http://en.wikipedia.org/wiki/Ohio_Scientific
http://classiccmp.org/dunfield/osi/index.htm
http://home.cmaaccess.com/~jerrytravis/
http://oldcomputers.net/osi-600.html
http://osi.marks-lab.com/
http://osiweb.org/osiweb/software.html
http://superboard.com.sapo.pt/
http://uk101.sourceforge.net/
http://www.6502.org/
http://www.6502.org/users/sjgray/computer/osi-c4p/
http://www.binarydinosaurs.co.uk/Museum/ohio/index.php
http://www.classic-computers.org.nz/collection/challenger1.htm
http://www.compukit.org/Compukit.org
http://www.cse.dmu.ac.uk/~mward/martin/software/index.html#UK101
http://www.gifford.co.uk/~coredump/uk101.htm
http://www.historyofpersonalcomputing.com/osi-superboard-i-and-ii/
http://www.lysator.liu.se/adventure/machines/OSI.html
http://www.neoncluster.com/projects-osi/osi-cassettes.html
http://www.old-computers.com/museum/computer.asp?c=572&st=1
http://www.old-computers.com/museum/computer.asp?c=860&st=1
http://www.oldcomputermuseum.com/superboard_2.html
http://www.osiweb.org/
http://www.pagetable.com/?p=43
http://www.pagetable.com/?p=46
http://www.pc-history.org/ohio.htm
http://www.technology.niagarac.on.ca/people/mcsele/OhioScientific.html
http://dabeaz.blogspot.co.uk/2010/08/using-python-to-encode-cassette.html
http://searle.hostei.com/grant/uk101/uk101.html
http://www.slideshare.net/dabeaz/using-python3-to-build-a-cloud-computing-service-for-my-superboard-ii
https://www.youtube.com/watch?v=pB2t6xG2RzE

Superboard ///:

http://forum.6502.org/viewtopic.php?f=8&t=2487
http://www.brielcomputers.com/phpBB3/viewtopic.php?f=39&t=1627
http://www.brielcomputers.com/wordpress/?cat=39
http://www.brielcomputers.com/wordpress/?cat=41
http://www.retrothing.com/2014/06/superboard-iii-briel-recreates-another-1970s-microcomputer.html

Heathkit RX-1 Recapping

I finished "recapping", i.e. replacing the paper capacitors in the Heathkit RX-1. Some were a little tricky to get at when the unit was assembled.

Here are some of the original caps:

And here is an image after recapping (the news ones are all yellow):



I didn't notice any significant difference after recapping, but it is still a good idea to do. Depending on the circuit location, a leaky capacitor can damage a tube or other expensive component. Below is all the old caps after removal:

Heathkit RX-1 Restoration

My latest restoration project is a Heathkit RX-1 "Mohawk" Amateur Radio Receiver.

I've created YouTube video that describes it. This was Heathkit's high end amateur radio receiver of the time, with all the bells and whistles of a radio of the time. It's a large beast, weighing in at about 50 pounds.

It works, but I'm currently in the process or recapping it, to make sure that it is fully functional. I'm replacing all of the wax paper capacitors with new ones, as the original ones tend to become electrically leaky over time. This may fix the operation of the notch filter, which doesn't seem to be fully working. The circuitry around the notch filter uses a lot of paper caps.

Once that is done I will run through the alignment procedure again. As it is quite an involved procedure, that might be suitable for another YouTube video of its own.

The Visible Monitor

While waiting for my Briel Superboard III kit, I was reminded of a book that I blogged about last year. The Visible Monitor program in that book was written to run on a number of computers of the era, including the Ohio Scientific C-1P or Superboard II.

In preparation for trying it on the Superboard III, I entered the machine code from the book. Back in the day, this consisted of typing in many numbers as BASIC DATA statements. A loader program read the data at run-time and stored it in memory. A simple checksum scheme caught most errors. After a number of sessions I had all the code entered. I was able to save some time by scanning the book pages and using OCR software to convert it to text, however the process was still quite error prone and required a lot of manual corrections.

After fixing any obvious errors, I was able to load the software on an Ohio Scientific computer emulator. The loader program found a number of additional errors that I had made. After correcting those, I made a file suitable for directly loading from the OSI monitor program. Loading it into the emulator, I was pleasantly surprised to see that it ran fine. I'm quite confident that it will also run on the real hardware.

I also entered some of the source code for the monitor with suitable changes to build with the CC65 assembler. I've only entered a small portion of the code so far, and may not complete this as it is a very time consuming task. All of the code can be found here at github.

By coincidence, a lot of vintage books I recently bought on eBay included the book "Top Down Assembly Language Programming for your VIC-20 and Commodore 64". It turns out that this is essentially the same book, but with the Visible Monitor ported to the VIC-20 and Commodore 64 computers.

To be honest, the Visible Monitor seems a little clunky and hard to use and I think my JMON program is better. I plan to port it to the Superboard III.

Zenith H500 Super Trans-Oceanic

The Zenith Trans-Oceanics were an extremely popular (although expensive) series of shortwave portable radios made by Zenith from the 1940s through 1980s. I own a model H500, the most popular model of the series. Although I restored it almost 10 years ago, I finally got around to making a YouTube video about it.

On the Heathkit front, I just received two more pieces of test equipment that I will be restoring, an IG-18 Sine-Square Audio Generator and an IM-1212 Digital Multimeter. I plan to make YouTube videos about these units as well.

Ohio Scientific Superboard II

The first computer I owned was an Ohio Scientific Superboard II. Bought in 1980, it was the only reasonably complete computer on the market for under $300.

I learned a lot on that machine, including BASIC and 6502 machine and assembly language programming.

Alas, it was damaged in a flood a number of years ago and had to be thrown out. I recently found this original paperwork which came with the machine:

I am, however, eagerly waiting the Superboard III.  a replica of the Superboard II that is being offered by Briel Computers. It should be fun to see the Superboard powered up again, running BASIC and the really primitive machine language monitor. I might even have some software I wrote on old cassette tapes that can still be recovered.

I'll report back here as the project progresses.