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PCE_Keyboard - PC Engine USB Japanese Keyboard Converter

Overview

This project is intended to allow use of a modern Japanese USB keyboard on a PC Engine. The board itself is the same as the one used for USB Mouse, but with different firmware.

PC Board and Assembly

I designed all boards using the free version of EAGLE (2-layer, less than 100mm on both X- and Y- axes). The gerbers are included in this repository, in case you want to get your own set made.

I have included the gerbers and relevant bom.csv and assembly.csv files to get these boards assembled by JLCPCB, but you will still need the following parts:

  • (1) Adafruit QtPy RP2040 microcontroller board
  • (2) 7-pin headers. You may also want to use female pin header sockets in case you need to remove the microcontroller board. I recommend using short/low-profile header sockets in this case.

Steps to assembly:

  1. Trim the leads of the through-hole parts carefully, to minimize the solder "bump" on the underside of the board when mounted. The through-hole parts to be mounted include the 8-pin mini-DIN socket, and the headers (or sockets) for the RP2040 board.
  2. Solder carefully, minimizing the amount of "bump" below the board
  3. Mount the RP2040 board with the USB connector facing away from the 8-pin DIN connector.
  4. Connect it to a host computer while holding the "Boot" button down. This will put it in DFU mode and create a virtual drive on the host computer. Drag and drop the *.uf2 firmware file into that folder. A moment later, the virtual drive should disappear and after about 1 second, all four LEDs should light up briefly as part of the boot sequence of the memory device. Disconnect it from USB.

Source Code

Compilation

This was updated to use Pico-SDK version 1.5.0 .

pico_sdk_import.cmake is from the SDK, but is required by CMake (and thus replicated here)

This is based on the TinyUSB Host HID example, and since this often changes (required by refactoring of the Host HID code), the initial commit baseline is the source ocde of that example.

To build the source, first ensure that you have the right version of the RaspberryPi/piso-sdk installed. As this board targets the Adafruit QtPy2040 board, you should run the make_ada.sh script (under UNIX). Then, "cd build" and "make".

I have also included a release version of the program as a uf2 file in the releases/ folder; just drag and drop it onto the virtual drive presented when putting the board into BOOTSEL mode (holding the 'boot' button, connect the board by USB to a host computer, and release the button; a new drive should appear on the computer).

Theory of Operation

At a high level, this is a multi-processor system, withe the division of work as follows:

  • CPU0 : perform USB scanning, and update an array of keypress/releases according to the PC Engine protocol
  • CPU1 : watch the incoming SEL and CLR lines in order to output the correct data over GPIOs

In this design, I opted not to use PIOs, as the GPIOs have a fast enough response time.

PCE Keyboard Protocol:

See the Technical section here

Key Mapping:

Japanese keyboard