On the Switch Science website, a "1-bit CPU assembly kit" that claims to be "the world's top low-performance computer" will go on sale from the 12th. It is priced at 2,500 yen (about 117 yuan), but it is currently sold out. MADE BY NAOTO.
While the world's fastest CPUs have been introduced, using cutting-edge processes like the Core Ultra and fifth-generation Xeon, this one is a counterclockwise product...... Or rather, the ultimate depraved product. The universal register is an astonishing 1 bit x 1, the address space is 2 bits, the address bus width is 1 bit, the ROM capacity is only 4 bits, and the program counter is also 1 bit.
There are two instruction sets: "ADD" and "JMP", and the only arithmetic operation is 1-bit addition (XOR). The clock frequency is about 1Hz. All you can do is "L blinking (LED flashing)", "LED on" and "LED off". That's it.
Naturally, you can't use a keyboard, mouse, monitor, etc., and operate it through the DIP switch on the board, and the results are only displayed on the LED. For example, if you want to create a program that constantly adds 1 to register A, simply set the DIP switch to "OFF/ON/ON/OFF" and use it as a mnemonic.
I bought one and did an experience.
There is nothing difficult to assemble
Although the kit requires welding, it is easy to assemble because there are not many parts. Basically, you can do it while looking at the finished photo, but be careful with polarized parts like LEDs.
The components used include the 2-input NAND gate "74HC00", the 6-circuit Schmitt flip-flop inverter "74HC14", the 2-circuit flip-flop "74HC74", and the dual-4-input multiplexer "74HC153". The component can be a USB Type-C connector for power delivery.
There are instructions that in order to avoid heat damage to the LEDs during soldering, float the LEDs, so bend the leads in the appropriate position and solder while fixing them.
The program has only 2 lines
These microcontroller kits are typically 4-bit or 8-bit and can be used to write simple games. However, this machine is a "1-bit computer" that has been declared "the world's top low-performance computer". So this game is a bit difficult (laughs).
There are many ways to think about how many bits a CPU should call, but in this suite, the universal register (A register) is 1 bit x 1, the address bus width determines the amount of memory that can be processed is also 1 bit, and the program counter that advances the address is also 1 bit as the target is loaded as the processing progresses.
The output is an LED that displays the binary information of the A register, and since there are two ways: on or off, this is also 1 bit.
The 1-bit address bus width means that there are only two addresses, 0 and 1, which means that only two lines of program can be written. Since there are two addresses, a 1-digit program counter is sufficient, which is an amazing (but natural) norm.
On the other hand, an address (word) is 1 bit in size and cannot represent both the opcode (instruction) and the subsequent operand (number or address), so 2 bits are retained.
Another factor that contributes to the low performance of this CPU is that it is clocked at 1Hz. Since it is "1Hz" and not 1GHz or 1MHz, the cycle is done every second. Even ENIAC, which is known as the originator of computers, is said to be able to complete one addition operation in 200 μs, which is 5,000 times faster with this kit alone.
Let's start coding!
Now, the machine is programmed in machine language, but there are only two instructions: "ADD (addition)" and "JMP (jump)". After each one, write the number to be added by the ADD command (0 or 1), or JMP to the address you want to jump to (0 or 1).
Use the DIP switch to set the instructions and data, which becomes the program. The ADD instruction is 0 (off) in machine language and the JMP instruction is 1 (on) in machine language. This DIP switch is a ROM, and since there are four switches, "ROM capacity = 4 bits".
Since there are few instructions and the data is only a binary number, you can only do "add one bit binary number" and "Lticker" (LED flashing), as stated in the manual.
The addition of one-bit binary numbers is done using mnemonics, a form of machine language that is easier for humans to read.
ADD A, 1JMP 1
(The first line is "Address 0" and the second line is "Address 1"). At this time, the DIP switch is set to OFF/ON/ON/ON. When you press the reset button and execute, the turned off A register LED (red) will light up on the next clock. This means that "0+1=1" has been calculated. "JMP 1" indicates that it is stuck at address 1, indicating the end of processing.
Next, L Chika mnemonic-
ADD A, 1JMP 0
So the DIP switch is off/on/on/off. Since 1 is added to address 0, the LED of register A is lit. Address 1 below means "return address 0", so register A plus 1. This is a binary number that means "1+1=10", but since the parts to be added can only handle 1 bit, the carry is ignored and becomes 0. Then add 1 and it becomes an L tick.
This "addition of one-bit binary numbers ignoring carrying" becomes "0+0=0", "0+1=1", "1+0=1", "1+1=0", and the logic gate "XOR" (XOR) itself. If you actually look at the circuit diagram, you'll see that it consists of an XOR gate that uses four NAND gates.
So, in simple terms, this CPU can be called a "XM-getter" (or a half-adder without carrying).
The 74HC74 chip is a D-type flip-flop with two circuits, each of which holds the value of the A register and the program counter. This can also be read from the circuit diagram.
By the way, this CPU seems to be designed to automatically return to address 0 and loop, unless you specify stop (JMP 1) at address 1 (line 2). The program -
ADD A, 1ADD A, 1
(Off/On/Off/On), adding 1 to register A is twice as fast as the previous L-code program, so the LEDs in register A continue to blink twice as fast.
That's why I'm interested in microcontrollers
When it comes to single-board computers, the latest version of the popular Raspberry Pi 5 is just getting started, and the specifications of this kit cannot be compared to those of this type of computer. I bought it this time for a joke, but when I first opened it up and started working, I was still impressed.
In addition to having too few instructions, the suite lacks basic CPU features such as flag registers and stack pointers. With that in mind, for the purpose of learning machine languages, such as the 4-bit microcomputer suite "ORANGE-4" (Picosoft) that I tried earlier, might be appropriate.
That said, this is probably the first and last time we've seen a CPU kit with a sharp 1-bit design, so I thought it would be fun to use it while feeling the origins of the computer, and I was interested in the principles and logic circuits of the CPU (microcomputer) that I felt was a good project. It's a simple design, so I thought it was interesting to study and try to understand the circuit diagram.
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