The MAX485 (now made by Analog Devices, and others) is the interface component you most often hear about, though there are other pin-compatible components from other manufacturers, and the old SN75176 (pre-CMOS) was the same. On the MAX485, A > B is treated as a 1, A < B is a 0. Another way to think about it is "When the output is active, A matches the input pin, B is the inverse of the input". That's the most common convention. And of course for the receive direction, "The received data matches A, and is inverted relative to B".

 

I have purchased different USB to RS485 converter USB-RS485Converter and it works without any problems. Thank you all for the support.

 

I have a problem with a hardware board where i do not receive the uart data but the board can transmit. The transceiver is SN65HVD08D, i have given 3.3V as supply to the transceiver, but the micro controller is 5V so the DE, UART Rx and Tx are all 5V from the microcontroller. i am testing using USB to RS485 converter connected to the PC. USB to RS485 Converter Module - leetechbd
View attachment 368915

when MPU output is 5V and the line driver =3v3.
The linedriver will clamp and could go defective.
Solution resistor (10K approx) connected between transmit pin in mpu and input line driver.
Place a fast diode between 3v3 and the input of the line driver.
the voltage on the line driver will be 3.3V-diode voltage.
Current in that circuit during MPU high (5-(3.3-.6)/10K = 0.23 mA approx so no risk.

.6 = voltage over diode in conducting state. check data sheet for zener used
line driver: rs485 chip.
input line driver: from mpu.
Remark: some use zener diode. However a zener is not fast and need more current.

Picbuster