Dakota Winslow

By

Dakota

·

Tiny Tapeout 5: Character Selector

An ASIC to display an alphanumeric character based on an 8-bit binary input

Character Selector Sim Output
Character Selector Sim Output

Design Objective

Tiny Tapeout is a program democratizing ASIC design by allowing students and other non-professionals to upload designs that eventually get etched into actual silicon. As part of a 24-hour hackathon, I submitted a design for Tiny Tapeout 5 in Nov 2023. I wanted my design to be unique, interactive, and simple enough to take advantage of the Wokwi visual logic editor. To that end, I designed a circuit that would display an alphanumeric character on a 7-segment display.

Execution

With only a few hours to devote to the project, I had to be clever about logic routing. Wokwi does not support bus connections, so every bit must be hand-wired. The 7+1 segment display used on the demo board has 8 inputs and each hardwired character circuit has 8 outputs. With 31 total characters, the number of connections tended to cause the editor to crash, so I retooled the design to to instead be based on a 1-wire signal, where a clock pulse would synchronize the transitions between each of the 8 positions on the display. Wokwi supports a 2:1 multiplexor module, but no demultplex, so I also had to hand build the demux from basic gates.

Results

Around 9 months after submission, the demo boards finally arrived. I am happy to say that my project worked! It is incredibly satisfying to see my design committed to actual silicon after all this time, and despite the very rushed development, I was able to produce a working design that satisfied my design goals.

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