Domorela's Blog: Modbus hardware interface

Modbus hardware interface is defined by the RS-485 standard, which determines two ways to interconnect Modbus devices: bus circuits using 4-Wire for Full Duplex communications or 2-Wire for Half Duplex communications.

The use of 2-Wire or 4-Wire installations doesn't prevent to interconnect 4-Wire Full Duplex devices to 2-Wire Half Duplex devices, it's possible to add 4-Wire devices to 2-Wire installations and the opposite. But it should be noted here that while a 2-Wire Master device cannot be connected to 4-Wire installations without resulting in data loss, it's always possible to connect a 4-Wire Full Duplex Master device to 2-Wire Half Duplex Modbus installations adapting the signals properly.

The above mentioned is the reason why Domorela, which is acting as a Master device when connected to the Modbus installation, includes a 4-Wire RS-485 hardware interface.

Thus, a Domorela DMRL1 unit can be directly connected as a Modbus Master device to 4-Wire Full Duplex Modbus installations. Being also possible to connect a Domorela DMRL1 unit to a 2-Wire Modbus installation, using an external adaptor or a repeater that will help for this purpose.

About handling connections, we chose to include a 4-Wire block connector in order to make easier to connect Domorela to the Modbus installation whether it is 4-Wire based or 2-Wire based.