The Sol-1: A 16-bit Computer In 74HC Logic With C Compiler And Unix-like OS

December 11, 2023 by Maya Posch 15 Comments

Sol-1 system pictured from the front. {Credit: Paulo Constantino)

While the concept of a computer system implemented in discrete logic ICs is by itself not among the most original ideas, the way some machines are executed certainly makes them stick out. This is the case with [Paulo Constantino]’s Sol-1, which not only looks extremely professional, but also comes with a lot of amenities that allow for system development, including a C compiler and assembler, a Unix-like OS (in development), DMA, and a whole host of interfaces to interact with the system and peripherals (serial, parallel, IDE, etc.). Not to mention a SystemVerilog model and an emulator, all of which can be found on [Paulo]’s GitHub.

More photos and videos can be found on [Paulo]’s YouTube channel, as well as the Sol-1 website, which shows off the intricate wire wrap work on the back of each PCB. In terms of the ISA, there are 5 general purpose registers (one scratch) which can also be used as two 8-bit registers each. Most operations are supported, except for floating point. For future improvements and additions, Sol-1’s OS will get more features added, and the first major software to be ported to the Sol-1 should be Colossal Cave Adventure and similar text-based adventure (dungeon) games.

A NOR Gate For An ALU?

April 5, 2023 by Jenny List 18 Comments

If you know anything about he design of a CPU, you’ll probably be able to identify that a critical component of all CPUs is the Arithmetic Logic Unit, or ALU. This is a collection of gates that can do a selection of binary operations, and which depending on the capabilities of the computer, can be a complex component. It’s a surprise then to find that a working CPU can be made with just a single NOR gate — which is what is at the heart of [Dennis Kuschel]’s My4th single board discrete logic computer. It’s the latest in a series of machines from him using the NOR ALU technique, and it replaces hardware complexity with extra software to perform complex operations.

Aside from a refreshingly simple and understandable circuit, it has 32k of RAM and a 32k EPROM, of which about 9k is microcode and the rest program. It’s called My4th because it has a Forth interpreter on board, and it has I2C and digital I/O as well as a serial port for its console.

This will never be a fast computer, but the fact that it computes at all is ts charm. In 2023 there are very few machines about that can be understood in their entirety, so this one is rather special even if it’s not the first 1-bit ALU we’ve seen.

Thanks [Ken Boak] for the tip.

A breadboard filled with logic chips and wiring

SPAM-1 Is A Well-Documented Discrete CPU With An Impressive Software Library

November 6, 2021 by Robin Kearey 16 Comments

Here at Hackaday we love projects that are so well-documented that you can spend days reading up on what the designer has achieved. [John Lonergan] didn’t disappoint when he designed the SPAM-1, an 8-bit CPU built from discrete logic gates. His detailed log contains a wealth of information on such things as designing opcodes, optimizing program counter logic, running a digital simulation, as well as his thoughts on microcode design. The sheer volume of it may be a bit off-putting to beginners, so it might be best to start with the video series that describes the architecture and goes into detail on several sub-blocks.

The design has changed a bit since [John] first started on the project, as he decided to add more and more features, but the final result is a well-thought out architecture that keeps the simplicity needed for discrete hardware but still has enough features to keep it interesting for seasoned CPU aficionados. The instruction size is rather large (48 bits) to simplify the instruction decoding at the expense of larger code size. Conditional jump instructions are not present; instead, all instructions have an optional control flag to make them conditional, a feature inspired by the ARM instruction set.

Once the design was mature enough, [John] modelled the entire thing in Verilog and simulated his design to verify correct operation and to check the timings, estimating it to be workable up to 5 MHz or so. A large stack of breadboards and DIP chips from the 74xx series then brought the design to life.

Not content with simply designing, simulating and implementing a custom CPU in hardware, [John] also spent significant effort on the software side of things, writing an assembler and even a C-like compiler for the SPAM-1 platform. And if that wasn’t enough, he also added an emulator for the classic CHIP-8 language, which allows it to run existing programs like Pong and Tetris. Input and output for all this software is mostly through a UART connection to a PC. A VGA interface is still on [John]’s to-do list, but he did build an adapter to connect a classic NES controller to the system.

The SPAM-1 is a worthy addition to the long list of discrete-logic CPUs we’ve seen here, such as this breadboard computer running a UNIX-like OS or this minimalistic one. If you’d like to see one that implements an existing instruction set, try this homebrew RISC-V computer.

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Incredible Discrete MOSFET Rover Has Maximum Blink

December 4, 2020 by Maya Posch 12 Comments

What do you get when you stick 1738 MOSFETs together? If your answer was a ‘4-bit CPU’, you would be totally correct. Available as a product over at Marutsu as the ‘CPU1738’, it seems to target beginners to computer theory, with build instructions that explain how the CPU is built up from individual MOSFETs that are combined into logic gates.

While decidedly more compact in its SMD format than it would have been with pure through-hole parts, the use of countless small PCBs on top of the larger PCBs make for a pretty hefty package. Board after board build up the CPU, and the assembly continues with the addition of sensors, motors, and wheels. In the end, a robot emerges, albeit a somewhat wobbly-looking one.

Check out the video linked after the break, though before starting one up, note the 50,000 Yen (approximately $500) price tag for the CPU block alone. On the other hand, in addition to the 1738 MOSFETs, there are also 1070 LEDs, so you get what you pay for in blinkies.

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