This is information about a "cheap" USB2CAN Adapter from China. It is based on a USB-Serial bridge (CP2102), a STM32F103 microcontroller and a NXP A1050 CAN transceiver. It came to me for approx. 15€. (See https://de.aliexpress.com/item/Free-shipping-CAN-Bus-Analyzer-USB-to-CAN-USB-CAN-debugger-adapter-communication-converter/32489958299.html for example).
I actually suggest NOT buying this device. Use a solution like CandleLight as that is a much more flexible approach, using a controller with USB and CAN in one (where even firmware with different USB implementations is available).
The device is USB powered via the regulator inside the CP2102. It is therefore able to provide ~75 mA to the application at 3.3V.
The USB interface is a CP2102 USB to serial bridge which allows 300bps to 1Mbps. The serial lines RXD and TXD are connected to the microcontroller.
The STM32F103C8T6 microcontroller is used. Pinout:
- PD0/PD1 (OSC_IN/OSC_OUT) to 12 MHz crystal
- NRST Open but fed via unplaced capacitor to GND
- PA0 feeds low side of red LED
- PA2/PA3 serial communication
- PA13 to J4.1 SWDIO
- PA14 to J4.2 SWCLK
- PB8/PB9 to CAN interface
- PB7 to /RST of CP2102 (RST I/O of CP2102 - will be low and can be driven low to reset)
- PB6 to /SUSPEND of CP2102 (CP2102 drives low when USB suspend is entered)
- BOOT0 to GND
Programming connector:
- J4: SWDIO SWCLK RST_NC 3,3V GND
The microcontroller is protected against readout, so I could not obtain the firmware via SWD.
STM32-SLCAN looks as if it could provide a working software. The clock settings need to be changed, because the original hardware uses a 12 MHz crystal. It needs libopencm3 to be obtained separately to compile.