Retro Computer Photographer Explores a Motorola 68K Educational Board with a Pi

With the help of a Raspberry Pi, Polish photographer and retro computer enthusiast Adam Podstawczynski re-captures the programming journey of a 1979-vintage Motorola 68000 Educational Computer board.

In the late 1970s and early 1980s, companies producing microprocessors generally developed an educational tool called a "trainer board" to go along with the chip. In some cases, these trainers were the bare minimum to form a computer system. These simplistic computers were prevalent in engineering classrooms, where students could explore the new world of 8-bit, and later 16-bit, processors. Generally, all a student had to do was hook up a dumb terminal's keyboard and display to the board to start programming it.

After Motorola introduced the 16-bit 68000 (68K) microprocessor, they introduced the Motorola 68000 Educational Computer Board or MEX68KECB for short. (Or ECB for even shorter.) It was an instant hit with educators.

The board featured a CPU running at 4 MHz, 32K of RAM, ROM (not flash!), a 24-bit programmable timer, GPIO, 7400-series control and multiplexer logic, an audio interface for cassette tape storage, and two RS-232 ports. The RS-232 ports let the user connect to a dumb terminal to interface with the ECB and to a host computer for sending and receiving code simultaneously.

Compared to today's Arduino boards, that list of features might seem mundane. But! Back in 1981, delighted engineers and students saw it as a full-featured computer! Just like a modern computer, the software was a huge component. Early computers had minimal "operating systems." The OS, or often just called "the monitor," had a kernel with just enough code to operate the onboard hardware. In the case of the ECB, it featured TUTOR.

TUTOR was a monitor program that enabled debugging, programming, loading code, and managing the RAM. Monitor programs like TUTOR let programmers explore any address in the RAM, execute assembly instructions, assemble assembly instructions into machine code, and even disassemble code out of memory.

Most importantly, TUTOR was the primary interface to program the board from a host computer. While a monitor might include a simple assembler, it was more common to use a more powerful microcomputer to write code and then program it into the ECB's RAM over RS-232.

That capability brings us to Podstawczynski's project. First, to add RS-232 (serial) and provide proper voltage conversions, Podstawczynski attached a HAT to give the Pi two ports: one to act as a dumb terminal and the other for programming. Then, he wrote a pair of Python scripts to send and receive data to the ECB from a Raspberry Pi. These scripts convert binary data into the format the TUTOR expects.

For full details, check out this Motorola 68000 Educational Computer Board post that includes the short explanation of the ECB, a log of getting the Pi connected, and the two Python scripts for interfacing with TUTOR.

Even if you do not have an ECB and a Pi, you might be interested in Podstawczynski's "Beauty Shots of Retro Machines" photo gallery. He captures vintage computers in a way that only a talented photographer could.