The OSI Model 300 Computer Trainer was advertised by Ohio Scientific Instruments in 1976 as a computer designed to introduce individuals to computers and teach them the basics of programming the MOS 6502 processor. The original trainer consists of a MOS 6502 processor, 6810 128 byte static RAM, one bit output latch, switches for entering data, and LEDs for reading the values of RAM.
The trainer was intended as a starter for individuals before moving on to their more advanced Model 400 Superboard system.
I first encountered one of these at VCFE 9.1 in 2014, and was intrigued by the simplicity of the design. I was particularly interested in the operation, and wanted to learn how the switches and LEDs were interfaced to perform the data read/write operations.
Get blistered fingertips from hand-jamming a few dozen machine instructions to calculate and display (on four LEDs) the 3141st digit of pi, only to have it all lost to a momentary power glitch?
We must suffer for our art. I'd certainly be tempted to toggle in not too much more than a loader, but that presumes some kind of peripheral to load from - there is none here. A pi program might only be a hundred bytes - most of the memory would be used for data. I accept the challenge!
At a quick glance the OSI-300 had some ... unique ... approaches to things ...
- Data bus was assumed to be high if left floating
- Writes to memory were not qualified with Phi-2 (in this case fair enough, but not a great template for the student of the 6502)
- No de-bounce on the reset - must have produced some interesting results from time to time
- that clock circuit
- No de-bounce on the NMI - wouldn't this confuse the interrupt handling in the CPU from time to time?
Talk abut being built down to a price.
However the tutorial in the manual was pretty good.
