SYSTEM DESIGN INFORMATION
12
4.1.4
MODBUS NETWORK INTERFACE
The FV300 can be a slave RTU device on a MODBUS network using a standard RS485 electrical
interface.
4.1.4.1
MODBUS COMMUNICATIONS PARAMETERS
Baud rate:
9,600 or 19,200 selectable.
Maximum number of units:
32
Protocol:
To MODBUS Application Protocol Specification V1.1 - See
‘Annex A for register definitions
Mode:
RTU
4.1.4.2
MODBUS LINE TERMINATION
The MODBUS network should have 390
Ω
bias resistors, to give defined voltage levels on the line,
and a 220
Ω
matching resistor fitted near to the controller, as shown below. In addition, a 220
Ω
termination should be fitted at the end of the pair cable to give reliable operation, especially with
long cable runs.
4.1.5
VIDEO OUTPUT
The FV300 provides a video output from the optional internal camera for connection to CCTV
systems. It is available in either PAL or NTSC format (option). The detector superimposes an
overlay with status information on top of the picture to notify alarms, including location, and faults.
The video output can be used on units without a camera to display the status information overlay
on a CCTV system. The status information is displayed on a coloured background. The output is
enabled by configuration.
The video output is a balanced signal suitable to drive twisted pair cable. The cable should be
terminated in a balun to provide the connection to the video system.
The video output operates over a reduced temperature range from -40 to +70°C. The detector
controls the video output to prevent damage if the temperature goes outside the range. See Table 1.
Output impedance:
100
Ω
into 100
Ω
twisted pair.
Receiving end:
Active balun NV - 652W (603.015.027).
+5V
MODBUS
CONTROLLER
0V
390
Ω
220
Ω
390
Ω
TWISTED
PAIR
DETECTOR
DETECTOR
220
Ω
Fig. 8
Line Termination
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