Source: https://mokxi.com/parts/ps2keyboard Updated: 2026-11-10 Part # PS/2 keyboard A real PS/2 keyboard on two wires, scan code set 2. Click it while it runs and type on it for real; Escape gives the keyboard back. See every part - 4 pins - In 1 project Drawn live by the editor's own code, at the size you see it. At a glance ## The PS/2 keyboard in brief What it is, and where it sits on the bench. A PS/2 keyboard needs only four wires, VCC, GND, CLK and DATA, and both signal lines are open collector with the pull-ups inside the keyboard, so the host uses two plain input pins and no resistors. The keyboard generates the clock and the host reads DATA on its falling edge, so CLK must go to an interrupt pin: 2 or 3 on an Uno, any GPIO on an ESP32. A real keyboard wants 5 volts; Mokxi works from 3.0 volts so a 3.3 volt board can power it directly, the one place it is more generous than the specification. Mokxi models the real eleven-bit frame (a start bit, eight data bits least significant first, odd parity and a stop bit) on a 12.5 kHz clock, scan code set 2 with 0xF0 break codes and 0xE0 prefixes, and the host-to-device half: Reset, Echo, Read ID, Set LEDs and the rest, with the 0xAA self-test reply 600 milliseconds. Click the keyboard and your own typing becomes scan codes; Escape gives it back. The classic mistake is CLK on a pin with no interrupt, which leaves the keyboard silent. Typematic repeat, the lock lamps, Print Screen and Pause are not modeled. Family Inputs Pins 4 Pins ## 4 pins Named as the editor names them, so a wire lands where you expect it. Pin What it does VCC Supply. GND Ground. CLK The clock, which the keyboard generates. Open collector. DATA The data line. Open collector. How to use it ## How to use a PS/2 keyboard with an Arduino Four wires: VCC, GND, CLK and DATA. Both signals are open collector with the pull-ups inside the keyboard, so they go to two plain input pins with no resistors. The keyboard makes the clock and the host reads DATA on its falling edge, so CLK must be on an interrupt pin: 2 or 3 on an Uno. The typewriter here is an ESP32-C3 board, where any GPIO will do, with CLK on GPIO 3 and DATA on GPIO 2. Click the keyboard while it runs and your own typing becomes set 2 scan codes; Escape gives it back. On an Uno the PS2Keyboard library’s begin(DataPin, IRQpin), available() and read() compile as they stand; note the data pin comes first. CLK on a pin with no interrupt is the fault everybody hits: the sketch is right and the keyboard is silent. Part pin Board pin CLK GPIO 3 DATA GPIO 2 VCC 3V3 GND GND A real PS/2 keyboard wants 5 V; the part works from 3.0 V so the ESP32-C3 can power it from 3V3 without 5 V on its pins. Click to open it in the editor This is the simulator itself, running here. Click anything to open it in the editor. Open this project in the editor Read the full tutorial The PS2Keyboard library on an Uno How it is modeled ## What is true about the PS/2 keyboard, here In its help article’s own words: what the simulation gets right, and where it stops. ### Modeled The frame is the real one: a start bit, eight data bits least significant first, an odd parity bit and a stop bit, with the keyboard generating the clock at 12.5 kHz (inside the 10 to 16.7 kHz the specification allows), the data settled 15 µs before the clock falls and the clock low for 40 µs, both inside their windows. The host reads DATA on the falling edge. Scan code set 2, which is what every PS/2 keyboard powers up in: a key pressed sends its make code, a key released sends 0xF0 then the same code, and the keys added after the original 84-key layout (the arrows, the navigation block, the right-hand modifiers, the keypad's / and Enter) carry an 0xE0 prefix in front of both, so releasing the up arrow is E0 F0 75. The host-to-device half is there too. Hold CLK down for more than 100 µs, pull DATA down and let CLK go, and the keyboard clocks eleven bits in, reading DATA on each rising edge, and pulls DATA down for a twelfth clock to acknowledge. It answers Reset (0xFF), Resend, Set defaults, Enable and Disable scanning, Set typematic rate, Read ID (0xFA 0xAB 0x83), Set scan code set, Echo and Set LEDs, and answers 0xFE to a command it does not know, which is what a keyboard does. It also runs the power-on self test and sends 0xAA six hundred milliseconds later, as the specification says. Holding the clock down inhibits it: a byte typed while the host has CLK low waits in the keyboard's buffer and goes out when the line comes back, rather than being lost. ### Not modeled Typematic repeat. A real keyboard repeats the last key held down after its typematic delay. This one has no timer for it. The repeat you see is your own computer's, arriving as more presses, which is what it looks like on the wire anyway. 0xF3 is accepted and its rate byte kept, and changes nothing. The lock lamps. 0xED is accepted and the three bits kept; there are no LEDs on the picture to light. Print Screen and Pause. Their set 2 sequences are the two multi-byte oddities (E0 12 E0 7C and E1 14 77 E1 F0 14 F0 77). There is no key for them on this part, so nothing here has to pretend to send them. The supply. A PS/2 keyboard is nominally a 5 V device; the connector carries 5 V ±10 %. This model works from 3.0 V up, so a 3.3 V board can drive one directly the way every ESP32 PS/2 sketch assumes. That is the one place the part is more generous than the specification, and it is deliberate: the alternative is an example circuit that puts 5 V signals on pins that are not 5 V tolerant. From PS/2 keyboard, in full. Projects ## See the PS/2 keyboard in a project One built-in project uses it. It opens in the editor, already wired. Boards ## The boards it is shown on This board has a built-in project with the PS/2 keyboard in it. - ESP32-C3-DevKitM-1 More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Filament lamp A tungsten bulb in a holder: an inrush when it is switched on cold, tens of milliseconds to warm up, and dim on half its voltage. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio; real internet through the Cloud panel’s switch), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. Raspberry Pi 4 Model B Raspberry Pi 4 Model B: the 40-pin header, driven by main.py with RPi.GPIO or gpiozero. See every part ## Wire up the PS/2 keyboard Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building free Open the editor