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
--
