24 • MRLDS-250 Infrared Gas Detector I&O Manual 026-1315 Rev 4
7 MODBUS
Communications
7.1. Introduction
The MRLDS-250 gas detector can be configured to
communicate on an RS-485 network using
MODBUS-RTU protocol. Before configuring the gas
detector for MODBUS communications, be sure your
network connection is complete and your network
termination switches are set appropriately. Refer to
Section 3, Wiring and Configuration for details.
7.2. Communications
Settings
There are 255 selections available to be set
electronically, from addresses 1 to 255 inclusive.
MODBUS data with a zero in the address field is
received by all detectors (regardless of the address
selected) to enable the master device to broadcast
simultaneously to all the detectors.
Refer to the specifications section for information on
RS-485 network communications parameters such as
data bits, stop bits, and more.
7.3. Analog Input Registers
Analog input registers are read only and use
function code 04.
Table 7-1 - Analog Input Registers
Reg Description Range Units P.-##
1000 Concentration gas level 0-100 %FS --
1001 Concentration gas level 0-65, 535 PPM --
1002
1003 Full scale detector level 0-65, 535 PPM --
1004 Alarm setpoint (% full
scale)
0-100 % --
1005 Gas detector timer 0-65, 535 hours --
1006 Node address 1-247 none P.-10
1007 Software version none --
1008 Reserved --
1009 Reserved --
1010 Reserved --
1011 Reserved --
1012 16-bit fault code 0-65535 none --
Reserved --
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