One measure of a pc’s bit width is the dimensions of the CPU’s registers. For instance, a number of early 8-bit house computer systems used an “8-bit” 6502 processor. And whereas computer systems later got here with 16-, 32-, 64-, and extra bits, a Japanese electronics maker referred to as naoto64 went the other way with the problem of constructing a 1-bit CPU with logic chips. This pc could be the head of low-performance computer systems as a result of it’s only able to two directions, leading to a blinking (or regular) LED.
The 1-bit CPU design makes use of 4 7400-series logic built-in circuits (ICs) to implement all the essential CPU blocks on the easy printed circuit board (PCB). The PCB additionally accommodates 4 dip switches, USB-C (for primary energy), 4 LEDs, and a push button.
On the core, a quad-NAND gate kinds an XOR-based arithmetic unit. In fact, this design means the 1-bit CPU solely has a single math operation: 1-bit ADD! Nonetheless, it additionally has a JMP instruction that enables repeated use of the exclusive-or. 4 dip switches make up the four-bit read-only reminiscence (ROM.) Three doable packages management the LED packages on, off, or toggling.
Why is that this a single-bit CPU? One aspect of the twin 7474 flip-flip kinds a 1-bit knowledge register, and the opposite kinds a program counter through the use of the output and its complement. Three gates of a 7414 (Schmitt Set off) inverter with passives create an approximate 1 Hz clock to drive the 1-bit CPU.
The spirit of this undertaking design reminds us of the MyNOR single-board pc. Dennis Kuschel constructed a floating level calculator round a CPU manufactured from solely a single NOR gate in that undertaking.
Whole 1-Bit CPU design (📷: naoto64)
The design is intelligent even when the 1-bit CPU doesn’t construct a sensible pc. Its schematic is value trying over. One of many extra spectacular elements of the design is that it absolutely makes use of all the weather within the 4 logic ICs!
The Japan-based on-line retailer Swap Science sells the 1-bit CPU equipment for 2500 Yen. You can too obtain the KiCad design information and Gerbers from naoto64’s GitHub repository. All of the documentation is in Japanese, however machine translation companies do a good job translating them.