Detcon 840 - Manual (Page 22)

840 Operators Manual
Model 840 Operator Manual Rev. 1.9 Page 18 of 29
7.
System Features
7.1 Modbus Communications
The model 840 controllers feature a Modbus compatible communications protocol and are addressable by a
PLC, PC/HMI, DCS, or other Modbus RTU master-polling devices. Communication is accomplished by
two wire half duplex RS-485, 9600 baud, 8 data bits, 1 stop bit, no parity, through the controllers secondary
port. Wiring should be brought directly to J10 located on the motherboard.
A Modbus™ RTU master device up to 4000 feet away can theoretically poll up to 64 different controllers.
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 controller must be set to a different device address.
Modbus™ Register Detail:
Code 03 - Read Holding Registers is the only code supported by the 840 controller.
Register #
40000
Channel 1 Reading
40001 Channel 2 Reading
40002 Channel 3 Reading
40003 Channel 4 Reading
40004 Channel 5 Reading
40005 Channel 6 Reading
40006 Channel 7 Reading
40007 Channel 8 Reading
40008 Fault Status Bits
High Byte
Bit 7
Not Used
Bit 6 Not Used
Bit 5 Not Used
Bit 4 Not Used
Bit 3 Not Used
Bit 2 Not Used
Bit 1 Not Used
Bit 0 Not Used
Low Byte
Bit 7
1 = Channel 8 Fault 0 = Channel 8 no Fault
Bit 6 1 = Channel 7 Fault 0 = Channel 7 no Fault
Bit 5 1 = Channel 6 Fault 0 = Channel 6 no Fault
Bit 4 1 = Channel 5 Fault 0 = Channel 5 no Fault
Bit 3 1 = Channel 4 Fault 0 = Channel 4 no Fault
Bit 2 1 = Channel 3 Fault 0 = Channel 3 no Fault
Bit 1 1 = Channel 2 Fault 0 = Channel 2 no Fault
Bit 0 1 = Channel 1 Fault 0 = Channel 1 no Fault
40009 Alarm 1 Status Bits
High Byte
Bit 7
Not Used
Bit 6 Not Used
Bit 5 Not Used