Arduino Uno R3 with DFRobot IO Expansion Shield

Hi there…

I’m trying to send and receive data through RS485. That’s why I’m choosing Arduino Uno R3 with DFRobot IO Expansion Shield.
I’m using this code in Arduino Uno R3 to send a byte.

byte data = {0x01};

Serial.write(data, 1);
delay(1000);
… and over and over again… every 1 second → send 0x01

So… I think I send 0x01. Then I connect it to my RS485 in my PC and try to read my serial port buffer (using C# SerialPort Class).

And what I get : 0x7F…?

Arduino send 0x01 → PC receive 0x7F
Arduino send 0x02 → PC receive 0x3F
Arduino send 0x11 → PC receive 0x77

Am I missing something here ???

And for the other direction (PC → Arduino), PC send 0x01 and Arduino receive nothing.
Serial.available() is always 0.

PS : During sketch upload, I remove the IO Expansion Shield. After upload finished, I put it again and set all 3 jumpers to RS485.

Can somebody help me ?

Then I connect it to my RS485 in my PC

Your PC has a RS485 jack?

Your post is missing links to the hardware you are using.

I have a USB-RS485 Converter in my PC. I check it again, and it’s ok, because I have another Industrial ADC and it use also Modbus RTU RS485. It works correctly. Only with Arduino is something wrong.

Buy from www.m-ware.de
Chipset is Prolific PL2303.