ps2pico

USB keyboard to PS/2+AT or XT interface converter using a Raspberry Pi Pico

Keyboard + Mouse variant: https://github.com/No0ne/ps2x2pico

Additional excellent documentation by Ray: https://minuszerodegrees.net/keyboard/ps2pico.htm

Usage

• Download ps2pico.uf2 or ps2pico-XT.uf2 from https://github.com/No0ne/ps2pico/releases
• Copy ps2pico.uf2 or ps2pico-XT.uf2 to your Pi Pico by pressing BOOTSEL before pluggging in.
• Afterwards connect a USB keyboard using an OTG-adapter and PS/2+AT or XT 5V to Pico VBUS.
• Also works with wireless keyboards with a dedicated USB receiver.
• 3.3V/5V conversion is done with two NPN transistors, two zener diodes and four resistors as shown below:

                 PS/2+AT / XT CLOCK
                       |           ____
                       |__________|10k |___________ GPIO 14
            ____       |          |____|     |
GPIO 15 ___|2k2 |____|/  BC547             __|__
           |____|    |\e                    / \  3V6
                       |                     |
                   ____|__GND________________|___


                 PS/2+AT / XT DATA
                       |          ____
                       |_________|10k |____________ GPIO 17
            ____       |         |____|      |
GPIO 16 ___|2k2 |____|/  BC547             __|__
           |____|    |\e                    / \  3V6
                       |                     |
                   ____|__GND________________|___

NuXTv2

If you have a NuXTv2 you can build an internal version of the ps2pico-XT! Replace U10 with the pico, remove RN13 and add two 4k7 pull-up resistors as shown below:

Build

export PICO_SDK_PATH=/path/to/pico-sdk
mkdir build
cd build
cmake ..
make

Resources

• https://wiki.osdev.org/PS/2_Keyboard
• https://github.com/Harvie/ps2dev/blob/master/src/ps2dev.cpp
• http://www.lucadavidian.com/2017/11/15/interfacing-ps2-keyboard-to-a-microcontroller/
• https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/translate.pdf
• https://github.com/tmk/tmk_keyboard/wiki/IBM-PC-XT-Keyboard-Protocol
• https://github.com/AndersBNielsen/pcxtkbd/blob/master/XT_KEYBOARD.ino