ABB UNITROL 1020 - Page 43

 Chapter 3 - Device Overview
UNITROL 1020 User Manual 3BHS335648 E82 35
3.3.9.3 RS485 Interface
UN1020 provides a RS485 interface for both VDC and Remote Access; however only
one can be operated with the RS485 interface. If both features are simultaneously
required, the solution is the usage of Remote Access over Modbus TCP and VDC over
RS485.
Figure 3-4 ABB solution if both Remote Access and VDC features are required.
The electrical connections of the RS485 bus should be performed according to EIA485
standard specification. The 120 Ohm resistor that is normally used to terminate a RS485
bus is already included in UN1020 and should be used by placing a jumper bridge over
the X1300 terminals. The X1300 location is shown in Chapter 3.3.2.4 Terminal Block.
Cable type requirements
 Cable cross-section: 2 x 0.25 mm
2
 Cable impedance: 100 to 120 Ohm
 Shielded twisted pair.
 500 m max cable length
(in case of UNITROL 1000-15 the bus is only 250 m)
Bus topology
 31 devices maximum for single channel and 62 for dual channel configuration.
 57.6 kBaud
The cable shielding shall be grounded as closely as possible to the device's terminals as
shown in the figure below.