ps2io – Support for PS/2 protocol

The ps2io module contains classes to provide PS/2 communication.


This module is not available in some SAMD21 builds. See the Module Support Matrix - Which Modules Are Available on Which Boards for more info.

All classes change hardware state and should be deinitialized when they are no longer needed if the program continues after use. To do so, either call deinit() or use a context manager. See Lifetime and ContextManagers for more info.

class ps2io.Ps2(data_pin: microcontroller.Pin, clock_pin: microcontroller.Pin)

Communicate with a PS/2 keyboard or mouse

Ps2 implements the PS/2 keyboard/mouse serial protocol, used in legacy devices. It is similar to UART but there are only two lines (Data and Clock). PS/2 devices are 5V, so bidirectional level converters must be used to connect the I/O lines to pins of 3.3V boards.

Create a Ps2 object associated with the given pins.

  • data_pin (Pin) – Pin tied to data wire.

  • clock_pin (Pin) – Pin tied to clock wire. This pin must support interrupts.

Read one byte from PS/2 keyboard and turn on Scroll Lock LED:

import ps2io
import board

kbd = ps2io.Ps2(board.D10, board.D11)

while len(kbd) == 0:


Deinitialises the Ps2 and releases any hardware resources for reuse.


No-op used by Context Managers.


Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.


Removes and returns the oldest received byte. When buffer is empty, raises an IndexError exception.

sendcmd(self, byte: int)int

Sends a command byte to PS/2. Returns the response byte, typically the general ack value (0xFA). Some commands return additional data which is available through popleft().

Raises a RuntimeError in case of failure. The root cause can be found by calling clear_errors(). It is advisable to call clear_errors() before sendcmd() to flush any previous errors.


byte (int) – byte value of the command


Returns and clears a bitmap with latest recorded communication errors.

Reception errors (arise asynchronously, as data is received):

0x01: start bit not 0

0x02: timeout

0x04: parity bit error

0x08: stop bit not 1

0x10: buffer overflow, newest data discarded

Transmission errors (can only arise in the course of sendcmd()):

0x100: clock pin didn’t go to LO in time

0x200: clock pin didn’t go to HI in time

0x400: data pin didn’t ACK

0x800: clock pin didn’t ACK

0x1000: device didn’t respond to RTS

0x2000: device didn’t send a response byte in time


Returns the number of received bytes in buffer, available to popleft().