1. Power indicator light: It is normally on when the power supply is normal
2. 3.3V/5V toggle switch: used to switch signal levels and VCC voltage. It is recommended to operate it when powered off.
3. CH343 serial port chip
4. RXD indicator light: Data reception indicator light, which flashes when data is being received at the TTL terminal.
5. TXD indicator: Data transmission indicator, flashes when data is being transmitted on the TTL port.
6. CTS indicator light: This is a transmission permission indicator light, which is constantly on when the input is valid.
7. RTS indicator light: Request to send indicator light, constantly on when outputting effectively.
8. VCC: Power output positive terminal, capable of outputting 5V/3.3V
9. RTS: Used to indicate that the device is ready to receive data, and is active when at a low voltage level.
10. CTS: Used to determine whether data can be sent to the other party, active low.
11. TXD: Serial data output
12. RXD: Serial Data Input
13. GND: Power output negative pole
14. RI: MODEM contact input signal, ringing indicator, active low
15. DSR: MODEM contact input signal, data device ready, active low
16. DTR: MODEM contact output signal, data terminal ready, active low
During power-on, if an external pull-down resistor is detected, it will switch to serial port transmission to indicate the status of ongoing operations, with high level being valid. 17. DCD: MODEM contact input signal, carrier detection, active low
18. DOWN: Pull-down resistor connection terminal.
During power-on, it can be connected to pins 16 and DTR via a dupont wire, switching it to the TNOW output pin to indicate that the serial port is sending data. In half-duplex mode, TNOW can be used to directly control the transmit-receive switching of the RS485 transceiver. 19. ACT: USB configuration completion status output, which can be used to notify the MCU or drive the light-emitting diode connected to VIO after a current-limiting resistor is connected in series. It is active at low level and inactive when suspended.