CH340 is an adapter chip of USB bus, which realizes USB to serial port or USB to printer port. Under serial port mode, CH340 provides common MODEM contact signal, which is used to extend asynchronous serial port for computer, or directly upgrade common serial port equipment to USB bus. Built-in firmware, software compatible with CH341, can directly use the VCP driver of CH341. Support 5V supply voltage, 3.3V supply voltage and even 3V supply voltage. CH340C/N/K/E and CH340B have built-in clocks without external crystal oscillator CH340 chip supports 5V supply voltage or 3.3V supply voltage. When the working voltage of 5V is used, the VCC pin of CH340 chip inputs an external 5V power supply, and the V3 pin should be externally connected with a power decoupling capacitor with a capacity of 0.1uF When a working voltage of 3.3V is used, The V3 pin of the CH340 chip should be connected to the VCC pin, and an external 3.3V power supply should be input at the same time, and the working voltage of other circuits connected to the CH340 chip should not exceed 3.3v. CH340 chip automatically supports USB device suspension to save power consumption. When NOS# pin is at low level, USB device suspension will be prohibited. DTR# pin of CH340 chip is used as the configuration input pin before the USB configuration is completed, and a 4.7KO ? pull-down resistor can be externally connected to generate the default low level during USB enumeration, and a larger power supply current can be applied to the USB bus through the configuration descriptor. The pins of CH340 chip in asynchronous serial mode include: data transmission pin, MODEM contact signal pin and auxiliary pin. Data transmission pins include TXD pins and RXD pins. RXD should be high when the serial port is idle. With respect to CH340G/C/T/R Chip

Common MODEM contact signals RTS, DTR, DCD, RI, DSR and CTS are supported. Hardware full-duplex serial port, built-in transceiver buffer, supports communication baud rate of 50 bps ~ 2 Mbps. The serial port application program under the Windows operating system of the computer is completely compatible and does not need to be modified. With additional level shifting devices, RS232, RS485, RS422 and other interfaces are provided. USB device interface at full speed, compatible with USB V2.0, The standard serial port is used to upgrade the original serial port peripheral equipment, or to add additional serial ports through USB.