Dual Zone Digital Location Control Unit Installation and Operation Manual
26
Modbus communications
The control unit includes a two-wire RS-485 Modbus output which (if enabled)
provides status information to third party equipment.
The Modbus RTU and ASCII protocols are both supported by the control unit.
Communications use the instructions and format shown below.
Function 4 code (Read Input Registers)
Requests for reading the input registers are constructed as follows:
• The address of the first register to be read (16-bit)
• The number of registers to be read (16-bit)
The control unit responds as follows:
• The number of bytes of register values to be read (8–bit)
• The register values (16-bit register)
The information stored in the control unit for each LHD zone is shown in the table
below.
Table 2: Modbus register values
Register
Description
Possible values
0
Zone 1 status
–1 or 65535 = fault on zone
0 = Zone OK
1 to 32767 = distance (in metres) to alarm point
1
Zone 2 status
–1 or 65535 = fault on zone
0 = Zone OK
1 to 32767 = distance (in metres) to alarm point
2
Zone 1 cable type
1 = 68
o
C
3 = 88
o
C
4 = 105
o
C
5 = 185
o
C
3
Zone 2 cable type
1 = 68
o
C
3 = 88
o
C
4 = 105
o
C
5 = 185
o
C
