Interface Rs-485; Interface Mode; Network Construction - Samson Trovis 6400 Mounting And Operating Instructions

Interface mode

9. Interface RS-485

The process control station can be optionally equipped with a serial RS-485 interface. This
interface enables the user to integrate TROVIS 6412 into a process control system and, by
means of a suitable software, establish a complete automation system for process control
applications. The hardware configuration needed for such an automation system is described
in section 9.2. The serial interface hardware meets the RS-485 (RS = Recommended Standard
acc. to EIA) requirements. Communication is based on the Modbus protocol. The functions
supported by the Modbus protocol are described in section 9.5. Other data are listed in the
table "Technical data", starting on page 8.
The RS-485 interface of the process control station is a PCB (printed circuit board) which is
installed in the associated slot of the controller case (see p. 13 , Fig. 5 ). If the TROVIS 6412
process control station is retrofitted with this interface board, proceed as described in section 9.6..
Fig. 7 , p. 22 and Fig. 9 , p. 24 show how to connect the data lines, based on the controller
case version used.
9.1. Interface mode
Several settings of the RS-485 interface are made by means of soldering jumpers. Please note
section 4.4., p. 20. The soldering jumpers on the interface board determine the baud rate, the
bus termination, two-wire or four-wire connection, and the character parity.
When the RS-485 interface is to be used for communication, the following parameters have to
be set in the Si level (See also section 6.6., p. 40).
– Station number (Address of process control station, range of values from 1 to 246)
– Timeout period (During this time, the central control station must have interrogated the
process control station at least once. Otherwise an error is indicated on the display of the
process control station. The Timeout period is only valid, when the status Timeout period
is switched on (see below); range of values: −1999 to −1 for minutes; 0.1 to 1999 for
seconds.)
Status Timeout period (Timeout period can be switched −on− or −oFF−)
–
Status RS-485 interface (switch interface mode −on− or −oFF−)
–
The interface mode is active as soon as the status RS-485 interface is switched on.
If internal communication between the process control station and the RS-485 interface is
interrupted, an error is indicated after 10 s. At the same time, the symbol
system not ready" flashes on the display.

9.2. Network construction

Fig. 40 shows an example how to construct a network for an automation system in which data
exchange is based on the Modbus protocol. A total amount of maximum 246 devices can be
interrogated. First a converter, which converts the RS-232 signal from the PC into a RS-485
signal, has to be connected to the PC. A repeater is to be provided if the connecting lines are
longer than 1200 m or more than 32 stations are connected to the bus. We recommend to
connect a maximum of three repeaters in series. In this way, the connecting lines can cover a
distance of up to 4800 m. A max. of 10 such lines can be connected in parallel when further
expanding the network. A bus termination is to be provided at the end of each line segment,
for example between converter and repeater, in order to discharge highly-resistive voltages.
60
Interface RS-485
for "external