Single board computers have been around for a long time: today you may be using a Raspberry Pi, Arduino or ESP32, but 30 years ago you may find yourself writing a KIM-1, Intel SDK-85 or Motorola 68000 educational computer board. Such boards are usually made by processor manufacturers to showcase their latest chips and train engineers who may use these chips in their designs.
[podstawek] I found myself trying to operate one of them Motorola European Central Bank Since 1981. The board contains a 68000 CPU (used in several Macintosh and Amigas), 32 kB of RAM and a ROM program called TUTOR. Without any keyboard or monitor connection, the only way to communicate with the system is a pair of serial ports. [podstawek] It was decided to make the board more accessible by adding a Raspberry Pi with RS232 hat extension. This add-on board has two serial ports and supports the +/- 12 V signal level used in older equipment.
It took several hours of experimenting, debugging, and reading a lot of ECB documents to establish a reliable connection; it turns out that the serial port can operate in different modes according to the state of the handshake line. When the Pi’s serial port was finally set to the correct mode, the old computer began to respond to commands entered in the terminal window. The audio interface used to record programs on tape proved to be more difficult to operate reliably, possibly due to aging capacitors. This is not a big problem, because the ECB’s second serial port can also be used to save and load programs directly into its memory.
As the serial connection works, [podstawek] Then turned to the aesthetics of his device, and decided to make a simple shell with laser-cut acrylic and metal gaskets. A custom ribbon cable for the serial port and an ATX breakout board for the power connection complete the project, and this 40-year-old educational computer is now ready to introduce all the details of 68000 programming to its new owner. In the video (embedded after the break), he showed the whole process of the European Central Bank’s startup and operation.
[podstawek] Previously used Commodore 64 and Arduino for similar clever settings. [Jeff Tranter] A similar 68000 development board was recreated from scratch. A few years ago, we even launched our own customized 68k computer.