Siebert SX102 Série Manuel D'utilisation page 31

Control via 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 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.
BAL SX102 MDB M 1.10 31