TraNOR's DIY Transistor Computer Has a CPU Design Containing 2,495 Discrete Transistors
An 8-bit computer capable of running up to 7MHz using discrete MOSFETs.
If you had 2,495 discrete MOSFETs sitting around unused, what would you create with them? Dennis Kuschel created an 8-bit computer system called TraNOR. It can run up to 7MHz, has an operating system, and can support modern interfaces like I2C and SPI.
We first found Kuschel's work when we wrote about the MyNOR. MyNOR is a 7400-series CPU design that used a single NOR-gate, made of two transistors, for its arithmetic logic unit (ALU). TraNOR is a software-compatible follow-on project that uses 2,495 discrete transistors for the entire CPU.
"This is not a transistor computer. In fact, it is a computer with a CPU made up of discrete transistors, and the CPU instructions are composed by microcode stored in the same memory that also contains the application program." — Creator, Dennis Kuschel
First off, as Kuschel says, TraNOR is not a 100% discrete computer design. The RAM, ROM, and LCD all use off-the-shelf ICs. Discrete transistors only make up the CPU and its I/O ports. The four 8-bit I/O ports use 598 transistors, while the rest of the 1,897 MOSFETs implement the CPU.
If transistor count demonstrates capability or power, then let's compare it to another popular 8-bit microcontroller. The efficient design of the venerable 8-bit 6502 microprocessor contains 3,218 transistors. For comparison to TraNOR, we have to ignore the I/O ports' MOSFETs since the 6502 does not have GPIO. TraNOR's CPU has just over half of the transistor count as a 6502: 1,897 vs. 3,218.
TraNOR can run up to 7MHz. At 4MHz, it is software-compatible with the MyNOR. Also, at this speed, its power consumption is only 4.5 watts!
Kuschel developed an operating system that contains some useful API functions. There is also a cross-assembler available for both Linux and Windows. Uploading new code, once assembled, is as simple as copy/paste into a terminal window. For software examples, jump to around 02:15 in the video demo below.
To build one, check out the download link at the bottom of the TraNOR page. There you can find the KiCad design files, instruction sets, and a document with the software APIs! You can also find information on additional peripherals like 10-bit sound output and LCD extension board.