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Mini version of the OSI-300 trainer

Mini version of the OSI-300 trainer

Here’s Christopher’s mini version of the OSI-300, he wrote a post on his blog detailing its assembly:

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.

Project info at