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USB to RS232 interface circuit diagram

Shenzhen STC Cable Manufacturer | Updated: Jul 05, 2017


Design USB to RS232 serial port hardware connection diagram The hardware system consists of four groups
Into: USB interface, CH341T, MAX232 and RS232 interface. Among  them, USB interface for connecting USB host, in this selection USB bus  interface type A connector; CH341T USB interface to RS232 interface for  all hardware functions; MAX232 for RS232 and TLL / CMOS level  conversion; RS232 interface for connecting RS232 devices. According to the actual needs, select the currently widely used DB9 connector.

    The USB bus includes a pair of 5V power lines and a pair of data signal lines. Normally, the + 5V power cord is
Red; ground wire is black; D + signal line is green; D-signal line is white. USB total
Line to provide the maximum supply current can reach 500 mA, CH341T chip can be used directly
USB bus provides 5V power supply. C3 and C4 are high frequency ceramic capacitors, C3 capacity is generally
4700pF ~ 0.02μF, for CH341T internal power supply node decoupling; C4 capacity of 0.1
ΜF is used for decoupling of external power supply. Crystal X1, capacitors C1 and C2 are used for clock oscillation
road. X1 frequency is 12 MHz, C1 and C2 is the capacity of 15 ~ 30 pF high-frequency ceramic capacitors

Circuit test

     A computer that connects to a USB-RS232 conversion card must have a CH341T driver installed
CH341SER.EXE,  when the module is first connected to the computer's USB port, the  computer prompts to find the new hardware, follow the prompts to  complete the driver installation. After installing the driver, you can provide the emulation serial port through the computer's USB interface. In  the logic function, the use of methods and ordinary computer serial  port exactly the same, support most of the commonly used serial  monitoring and debugging tool program, the application can not make any  changes, you can access a standard physical serial port as access to the  virtual serial port, Keep the hardware and software compatible under the premise of the original serial port products into USB interface. Is the use of "serial debugging assistant" software on the converter communication test results as shown. During  the test, the virtual port is COM3 after connecting the converter to  the computer, and the converter is connected with the COM1 port of  another computer by RS232 standard cable. The communication uses baud rate of 9600, 8 bit data bits, 1  stop bit, no parity bit, 2 ports automatically send data every 1000 ms.
       It can be seen that the converter is able to communicate reliably between USB / RS232 ports on different computers. In addition, the use of two converters, can achieve different computer USB communication, the test work is reliable.



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