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MGS-402 User Manual
5. Modbus
5.1 Modbus Overview
Modbus RTU protocol is utilized both for down line detector communication and up line BMS communication.
Communication parameters may be set via the configuration switches.
The MGS-402 controller acts as a Modbus master device on the detector side, and as a Modbus slave device
on the BMS side. Refer to the MODBUS tables found on page 15.
5.1.1 SLAVE NODE ADDRESS
This is the Modbus node address (10, 20, 30, 40, 50, 60, 70 or 80) that the upstream BMS will need to use
when sending queries to the controller.
5.1.2 SLAVE BAUD RATE
The MGS-402 controller will us this baud rate to communicate with the upstream BMS or Modbus master
device, either 9600 (default) or 19200.
5.1.3 SLAVE PARITY
This PARITY setting should match the BMS PARITY (NONE, EVEN or ODD).
5.1.4 SLAVE STOP BIT
The number of stop bits (1 or 2) must match the BMS setting.
5.1.5 SLAVE TERMINATION
A 120 ohm termination resistor can be enabled on the BMS connection. This is typically only required for
cable lengths in excess of 1,000 ft (304 m), for shorter distances set this termination to OUT.
5.2 Modbus Registers
Register
Address
R
X
30001
R
X
30002
Func Code 04
(read input registers)
Sensor 1 is monitored flag
Sensor 1 communication status Sensor 1
Item Group
Sensor 1
0 = Not Monitored
1 = Monitored
1 = Normal
2 = Failsafe
1100-2570 Rev 1
Notes
19
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