Saturday, January 31, 2015

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:

Ohio Scientific:

Superboard ///: