One measure of a pc’s bit width is the scale 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 often called naoto64 went the wrong way with the problem of constructing a 1-bit CPU with logic chips. This pc is perhaps the top of low-performance computer systems as a result of it is just 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 fundamental CPU blocks on the straightforward printed circuit board (PCB). The PCB additionally incorporates 4 dip switches, USB-C (for primary energy), 4 LEDs, and a push button.
On the core, a quad-NAND gate types an XOR-based arithmetic unit. After all, this design means the 1-bit CPU solely has a single math operation: 1-bit ADD! Nonetheless, it additionally has a JMP instruction that permits repeated use of the exclusive-or. 4 dip switches make up the four-bit read-only reminiscence (ROM.) Three doable applications management the LED applications on, off, or toggling.
Why is that this a single-bit CPU? One ingredient of the twin 7474 flip-flip types a 1-bit knowledge register, and the opposite types a program counter by utilizing 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 points of the design is that it totally makes use of all the weather within the 4 logic ICs!
The Japan-based on-line retailer Change Science sells the 1-bit CPU equipment for 2500 Yen. It’s also possible to 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.
