Palm® Portable Keyboard USB conversion

Setup

Sources for pinouts and extra info can be found in the Sources segment.

Building

Requires:

• probe-rs (or any other tool that can program an STM32 MCU)
• cargo (best if installed through rustup)
• an ST-Link USB probe
• an STM32F4 dev board (I used the Black Pill V3, it costs like 8 bucks)
• a Palm® Portable Keyboard (duh)

Connect the ST-Link to your STM32's SWD port without connecting the 3.3V pin and a USB cable to your dev board's USB port and run cargo run --release --features=defmt

Pin setup

B8 -> VCC pin

GND -> GND pin

B4 -> DCD/HotSync pin

B3 -> RTS pin

A3 -> RXD pin

The signal from the keyboard's RXD pin requires a 100k pull-up resistor and MUST then be passed through a NOT gate, since the STM32F411CEUx I used doesn't support the inverted USART signal that is given out by the keyboard

Connector

TO-DO :P

Alternate functions

Some keys have alternate functions that are triggered by pressing them along with Fn

• TO-DO

Sources

• Info on pinouts, protocols and the matrix layout used by the keyboard were referenced from here ¹

• JSON-formatted HID codes acquired from this gist ²

<sup>1. Some of the info on there isn't *quite* correct; although it states that the signal on the RXD line is at "RS-232 level", in the real world, it turns out that it's only regular ~3.3V inverted USART
2. "Keyboard International4" was accidentally labeled as "Keyboard International5" and was fixed in this repo</sup>