Siebert S102 Série Mode D'emploi page 30

Control via a RS485 2-wire bus
Control via RS485 2-wire bus (two-wire Modbus definition) as described as follows is
recommended by Modbus over serial line specification and implementation guide.
In menu item 1 setting 485.2 is to be selected.
Control via a RS485 4-wire bus
As an option interfacing can be effected via a 4-wire bus (optional four-wire Modbus
definition) as described as follows.
In menu item 1 setting 485.4 is to be selected.
Point-to-Point control
If the Modbus only consists of one master and one display as described as follows, in
menu item 1 setting 485 can also be selected.
30 BAL S102 MDB M 1.0