WCH CH9325
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The CH9325 is a USB interface chip, which converts data received via UART to USB and vice versa. The chip presents a HID (Human Interface Device) USB profile, in an effort to not require USB driver installation: this is typically handled by the OS kernel. An example of the profile, in Linux 'lsusb' output format, is here.
The chip runs off of a 12MHz oscillator.
Pin layout
| 1- | O | -16 | ||
| UART TX | 2- | -15 | USB +5V | |
| UART RX | 3- | -14 | ||
| 4- | -13 | |||
| 5- | -12 | |||
| USB D+ | 6- | -11 | ||
| USB D- | 7- | -10 | OSC+ | |
| GND | 8- | -9 | OSC- |
Protocol
The chip encodes what it receives on the UART RX pin into HID packets of 8 bytes.