keychron_qmk_firmware/converter/ps2_usb

PS/2 to USB keyboard converter

This firmware converts PS/2 keyboard protocol to USB and supports only Scan Code Set 2.

PS/2 signal handling implementations

Following three methods are used to implement PS/2 signal handling.

Simple and stupid busy-wait(ps2_busywait.c)

This is expected to implemented with portable C code for reference.

Interrupt driven(ps2_interrupt.c)

Uses pin interrupt to detect falling edge of clock line.

USART hardware module(ps2_usart.c)

Uses AVR USART engine to receive PS/2 signal.

To select method edit Makefile.

Connect Wires

In case of Teensy2.0(ATMega32U4):

1. Connect Vcc and GND.
2. Connect Clock and Data line.
   • Busywait: Clock is on PD5 and Data on PD2.
   • Interrupt: Clock is on PD1 and Data on PD2.
   • USART: Clock is on PD5 and Data on PD2.
3. Optionally you need pull-up register. 1K-10K Ohm is OK.

To change pin configuration edit config.h.

Build Firmware

Just run make:

$ make

To select keymap:

$ make KEYMAP=[plain|jis|spacefn|...]

Keymap

Several version of keymap are available in advance but you are recommended to define your favorite layout yourself. To define your own keymap create file named keymap_<name>.c and see keymap document(you can find in top README.md) and existent keymap files.

V-USB Support

You can also use this converter on ATmega(168/328) with V-USB instead of Teensy. The converter on V-USB lacks some features for now: USB NKRO and System/Media control.

Circuit:

                +---+   +---------------+
USB            GND  |   |   ATmega168   |
===                 C3  |               |
5V <-------+--------+---|Vcc,AVCC       |        PS/2
           R1           |               |        ====
D- <----+--+-----R2-----|INT1        RXD|------->DATA
D+ <----|---+----R3-----|INT0        XCK|------->CLOCK
        Z1  Z2          |               |      ->5V
GND<----+---+--+--+-----|GND            |      ->GND
               |  |     |               |
               |  C2-+--|XTAL1          |
               |     X1 |               |
               +--C3-+--|XTAL2          |
                        +---------------+
R1:     1.5K Ohm
R2,R3:  68 Ohm
Z1,Z2:  Zenner 3.6V
C1,C2:  22pF
C3:     0.1uF
X1:     Crystal 20MHz(16MHz/12MHz)