WIZ750SR can change serial mode by changing only one part from one module.
First of all, I can not use two functions together.
The reason is that both functions are connected to one UART0.
If you want to use two serial ports with WIZ750SR, you can use Simple UART (UART2) for communication.
However, since the port is usually used as a Debug port, it needs to be modified.
In order to use Serial to Ethernet function with UART2, it is necessary to modify the code.
Please refer to the image below for information on changing parts of the WIZ750SR.
Since WIZ750SR-TTL communicates with TTL level, it connects with resistance.
Since WIZ750SR-RS232 needs to convert to RS-232C level, RS-232C Transceiver must be built in.
Since WIZ750SR-RS485 must be used with RS-422/485, RS485 Transceiver must be built in.