I2C to Dual UART - DFR0627 - issue with modbus

Hello,

I have the DFR0627 module connected to my nRF52840 Adafruit Feather. I tested the module following the examples on https://wiki.dfrobot.com/Gravity%3A%20IIC%20to%20Dual%20UART%20Module%20SKU%3A%20DFR0627 and confirmed that it is working fine.

However, I was trying to communicate  from UART1  to an external sensor via Modbus and RS-485 to TTL converted board but it did not work, the code crashed. 

I am using “ModbusMaster” library on Arduino and did some modifications on it to support the DFRobot_IICSerial class but still couldn't figure it out.

Does this module (the DFR0627) support Modbus communication  via RS-485 ? 

Thank you.