OLCT 700/710 TP
OLCT 700/710 TP Instruction Manual Rev. C.1 Page 27 of 45
4. RS-485 Modbus™ Protocol
OLCT 700/710 gas detectors feature Modbus™ compatible communications protocol and are addressable
via the program mode. Communication is two wire, half duplex 485, 9600 baud, 8 data bits, 1 stop bit, no
parity, with the detector set up as a slave device. A master controller up to 1200 meters (4000 feet) away
can theoretically poll up to 256 different detectors. This number may not be realistic in harsh environments
where noise and/or wiring conditions would make it impractical to place so many devices on the same pair
of wires. If a multi-point system is being utilized, each detector should be set for a different address.
Typical address settings are: 01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11…etc.
Detector RS-485 ID numbers are factory default to 01. These can be changed in the field via the Operator
Interface described in Section 3.5.5 Set Serial ID.
The following section explains the details of the Modbus™ protocol that the OLCT 700/710 detector
supports.
Code 03 - Read Holding Registers is the only code supported by the transmitter. Each transmitter contains
6 holding registers which reflect its current status.
Table 3: Modbus™ Registers
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