UART hardware loopback.

This hardware causes UART to loop back at the hardware level. Developed based on the STM32F042 and CH340 chips, it taps the serial communication of the target software using the baud-rate auto-negotiation function of VCP.

In addition, since the pins of the 'SL2.1A' chip are left, so I added the USB hub function to utilize them. and 'PD (Power Delivery)' input in case the current is insufficient.

Hardware:

Schematic:

How to connect:

Requirements:

1. UART hardware loopback board with USB Type-C cable.
2. Target hardware and software.
3. This tapping software.

Steps to configure the hardware:

1. Connect the data cable, USB Type-C to your PC,
2. Attach a COM port of F042VCP to target software.
3. Then, attach a COM port of CH340 to this tapping software.
4. And, configure this tapping software to communicate with the target hardware.

Flashing the firmware:

This board's SL2.1A USB hub chip seems like that disable the SWD pins. (This seems to be a problem that occurs when the DP/DM pins wired on the board activate DFU mode or probe-like something) So, you can flash the F042F6P6 chip like:

Set-up pull resistor to BOOT0.

This enables ST-Link SWD pins. if BOOT0 pin is floating, the chip will never enable DFU or SWD pins.

• BOOT0 -> pull down: enables SWD.
• BOOT0 -> pull up: enables DFU.

Using development board prototype.

Solder the F042F6P6 chip to development board or use non-solder programming tools, and flash your chip, then re-solder it to this board.

USB DFU mode.

Initially, the F042F6P6 chip will be booted in DFU mode.

1. download DfuSe tool from ST microelectronics website: https://www.st.com/content/my_st_com/en/products/development-tools/software-development-tools/stm32-software-development-tools/stm32-programmers/stsw-stm32080.license=1635064983409.product=STSW-STM32080.version=3.0.6.html#get-software

2. install it and goto [System drive]:\Program Files (x86)\STMicroelectronics\Software\DfuSe v3.0.6\Bin using explorer.

3. double click DfuFileMgr.exe

4. check first option, I want to GENERATE a DFU file from S19, HEX or BIN files then click next.

5. put DF11 to Product ID field.

6. click S19 or Hex... button then, select your built HEX file, and click Generate.

7. close DFU File Manager tool, and double click DfuSeDemo.exe file.

8. select STM device in DFU mode from Available DFU Devices combo box.

9. click Choose... button on Upgrade or Verify Action panel.

10. select DFU file that generated at 6th process, then click Upgrade.

11. finally, click Leave DFU mode on Available DFU Devices panel.

12. unplug your board and re-plug it.

13. done.