I recently made a few updates to the TRHMSX project for version 1.51. Why 1.51? A last-minute issue in v1.5 led me to make additional tweaks, so here we are! Two recurring concerns from friends building the hardware or purchasing it to support my other MSX projects were:
- The composite video signal quality over the RCA jack.
- The increasing difficulty of finding USB keyboards compatible with the PS/2 protocol or those with PS/2 connectors.
Improved Video Quality with S-Video
To tackle video quality, I removed the composite connector and re-routed the signals to an S-Video mini-DIN connector. The signal is perfectly suited for S-Video, and the result is a significant improvement in video clarity compared to the previous version.
Note: If you built version 1.5, the S-Video signals were mistakenly inverted. This issue has been corrected in v1.51, so ensure you’re using the updated version for S-Video functionality.
To enable S-Video output, turn off switches 2 and 3 on the dip switch bank on the side of the computer.
Enhanced USB Keyboard Support
Adding support for USB keyboards was more challenging. While there are many USB-to-PS/2 solutions—such as Raspberry Pi Pico or Arduino-based converters—I opted for a robust, community-driven solution.
I implemented the circuit from the HIDMAN micro project by @serisman, based on the original HIDMAN by Andy (@rasteri). The solution uses the CH559 microcontroller from WCH (Nanjing QinHeng Electronics), a versatile 8051-based chip designed for USB applications.
The HIDMAN micro hardware and firmware offer a reliable way to adapt USB keyboards for PS/2 devices. Open-source hardware truly shines here, allowing to build on the amazing work of the community. Huge thanks to @rasteri and @serisman for their contributions!
Programming the CH559 Microcontroller
To enable USB keyboard support, you’ll need to program the CH559 microcontroller. Here’s how:
- Prepare Your Tools:
- Download the WCH ISP Tool from WCH’s website or from the TRHMSX GitHub repository if needed.
- For macOS or Linux, install the ch55xtool.
- Connect Your Hardware:
- Power off the TRHMSX.
- Use a USB A-to-A cable to connect the TRHMSX to your computer.
- Program the MCU:
- Launch the WCH ISP Tool and select the E8051 USB MCUs family.
- Ensure the CH559 model is detected. If it isn’t, check the chip installation or bootloader status.
- Download the pre-configured firmware for TRHMSX from the GitHub repository:
trhmsx/hardware/1.5/hidman-micro/firmware/dist. - Follow the tool’s prompts to upload the firmware. Please refer to the following images for the tool configuration.
After programming, USB keyboard support will be enabled. Note that some advanced keyboards with extra features may still require custom drivers.
Wrapping Up
These updates significantly enhance the TRHMSX’s functionality. Whether you’re enjoying better video quality via S-Video or a broader range of USB keyboards.
As always, the community’s feedback and support drive these improvements.
Enjoy your TRHMSX v1.51!