10PCS Pack of USB to 4 Way TTL Module CH9344 12Mbps Baud Rate UART Serial Port Module UART Transceiver 3.3V

CLOCK SIGNAL GENERATION: The clock signal can be generated through crystal stabilized oscillation through built in inverter of this module. The circuit requires a 30MHz crystal to be connected between pins x1 and X0, with X1 and x0 pins grounded to 20pF oscillating capacitor.
POWER ON RESET CIRCUIT: The CH9344 chip has built in power on reset circuit, which requires an external 30MHz clock signal to be provided to the x1 pin during normal operation.
PC CONNECTION: UD + and UD pins can be directly connected to PC or other USB host. If the fuse resistance or inductance or ESD protection device is connected in series for chip safety, the AC DC equivalent series resistance should be within 5°.
COMPLETE CIRCUIT: CH9344 chip has built in all circuits required by USB bus, including embedded USB2.0 controller and USB PHY, serial matching resistance of USB signal line, 1.5K pull up resistor required by device, etc.
POWER SUPPLY: The CH9344 chip and USB products can directly use 3.3V power supply output by VBUS on the USB bus after LDO stabilization. If the USB product provides a standby power supply through other power supply methods, CH9344 should also use this standby power supply to avoid 10 current backflow with the USB power supply.