Pi Pico Becomes SRAM for 1981 Educational Computer
Originally published on hackaday.com by Robin Kearey on 10 September 2023
Since its introduction in early 2021, the Raspberry Pi Pico has found its way into a wide range of applications, powering clocks, gadgets, games, and accessories for both old and new computers. Michael Wessel recently found a unique use for the Pico by turning it into a 2114 SRAM emulator for the Busch 2090, an educational computer system dating back to 1981.
The 2114 SRAM chip’s pinout is relatively straightforward, featuring ten address lines, four data lines, Write Enable, and Chip Select. Although the 3.3V Pico is somewhat 5V tolerant, Michael opted for greater reliability by using level shifters to bridge the two voltage domains. He experimented with standard level shifter circuits but also accounted for the Busch 2090’s 33 kΩ pulldown resistors on the address bus. By adding a couple of resistors to the Pico’s ports, he created entirely passive level shifters, which worked effectively given the system’s 500 kHz clock frequency.
In a video demonstration, Michael showcases the RAM replacement, complete with a set of blinkenlights illustrating real-time data transfer. He has plans to develop a proper PCB for his project and enable various features by modifying the system’s RAM in real-time. This PicoRAM emulator isn’t limited to the Busch 2090, as the 2114 chip was prevalent in 1980s systems, making it adaptable to other systems of that era. For those interested in trying it themselves, the Pi code is available on GitHub. If you’re curious about programming a Busch 2090, you can emulate one using an Arduino.
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