CH341A PDF – EEPROM Flash BIOS USB Programmer

This post explains for the USB-Interface-Chip. A USB bus converter chip, also known as a USB-to-serial converter chip, is an integrated circuit designed to interface between a Universal Serial Bus (USB) port and a serial communication protocol. This type of chip is commonly used to connect devices that communicate using serial protocols (like UART, RS-232, or RS-485) to a computer or other devices equipped with USB ports.

The Part Number is CH341A.

The function of this semiconductor is USB bus convert chip for EEPROM Flash BIOS USB Programmer.

The Package is DIP, SSOP 28 Pin

Manufacturer: Nanjing Qinheng Microelectronics ( )

See the preview image and the CH341A datasheet PDF file for more information.


CH341A datasheet


The CH341A is a USB bus convert chip, providing UART, printer port, parallel and synchronous serial with 2-wire or 4-wire through USB bus. In UART mode, CH341 provides alternant rate control signals such as serial transfer enable, serial receive in ready etc.

It also supplies common MODEM communication signal in order to expand UART for computer or upgrade common synchronous interface device to USB bus directly. In printer port mode, CH341 supplies standard USB printer port which compounds USB relevant protocol and Windows operate system used to upgrade ordinary parallel printer to USB bus directly. In parallel mode, CH341 gives out 8-bit parallel in EPP or MEM mode.  […]

CH341A pdf

Reference Site: CH341A Programmer : 8 Steps – Instructables


1. Full speed USB device interface, conforms to USB Specification Version 2.0, only needs crystal and
capacitance external.

2. Optional: define Vender ID, production ID and list number through external low-cost serial EEPROM.

3. Supports 5V and 3.3V power source.

4. Low-cost, directly convert serial peripheral equipment, parallel printer and parallel peripheral

CH341A pinout

1. Simulate standard serial used to upgrade serial peripheral equipment or increase extra serial via USB.

2. Totally compatible with serial application program of computer Windows operation system.

3. Hardware full-duplex serial, on-chip transform and receive buffer, supports 50bps~2Mbps communication baud rate.

CH341A PDF Datasheet

CH340 Datasheet – USB to Serial Chip (CH340G)

Part Number: CH340

Function: USB to serial chip

Package: SSOP-20 Type

Manufacturer: WCH ( )

This post explains for the semiconductor CH340.

Image :



CH340 is a USB bus convert chip and it can realize USB convert to serial interface, USB convert to IrDA infrared or USB convert to printer interface. In serial interface mode, CH340 supplies common MODEM liaison signal, used to enlarge asynchronous serial interface of computer or upgrade the common serial device to USBbus directly. More detail about USB convert to printer interface please referring to the second manual CH340DS2. In infrared mode, add infrared transceiver to CH340 can compose USB infrared adapter, realize SIR nfrared communication. The CH340 chip can be used with a variety of programming languages, including C, C++, Python, and others.


CH340 Pinout




1. Full speed USB device interface, conforms to USB Specification Version 2.0, only needs crystal and capacitance external.

2. Emulate standard serial interface, used to upgrade the former peripheral device, or add excess serial interface through USB.

3. Totally compatible with serial application program in computer endpoint Windows operation system.

4. Hardware full duplex serial interface, set transceiver buffer, supports communication baud rate varies from 50bps to 2Mbps.

5. Supports common MODEM liaison signal RTS, DTR, DCD, RI, DSR and CTS.

6. Through adding level converter equipment to supply RS232, RS485, RS422 and other interface.

7. Supports IrDA criterion SIR infrared communication, supports baud rate varies from 2400bps to

8. For it is through USB converts to serial interface, only compatible with application layer not totally.

9. Software compatible with CH341, using drive of CH341 directly.

10. Support 5V and 3.3V source voltage.


Block Diagram



Function description

CH340 sets up USB pull-up resistor internal, UD+ and UD- must be connected to USB bus.
CH340 set power up reset circuit. RSTI is used to input asynchronous reset signal from outside.

When RSTI is high-level, CH340 chip is reset. When RSTI is low-level, CH340 will continue delay 20mS to reset and then step into normal work state. In order to reset credibly during power up period and weaken the disturber from outside, a 0.47uF capacitance between RSTI and VCC is recommended.

When CH340 chip is working normally, the outside must supply 12MHz clock signal to XI pin.
In generally, clock signal is generated by inverter in CH340 through oscillating of crystal keeping frequency. A crystal of 12MHz between XI and XO, XI and XO connect a high frequency oscillator capacitance to ground respectively can compose the peripheral circuit.


Reference Site:

Other data sheets are available within the file: CH340G, CH340R, CH340T

CH340 Datasheet

CH340 pdf



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