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Modbus Master and Slave Modes
The DMS-3K support both Modbus Master and Modbus Slave Modes for Modbus Alarms and
Modbus Events.
Modbus Alarms
In Modbus Slave Mode, the DMS-3K provides up to eight 16-bit registers for a total of 128
inputs and one register for pushbutton controls to a single Modbus Master.
In Modbus Master Mode, the DMS-3K provides up to eight 16-bit registers for a total of 128
inputs and one register for pushbutton controls per Modbus Slave Device. This can be repeated
for up to 6 slave devices using serial communications and up to 8 slave devices when using
Ethernet (Modbus TCP/IP) communications.
Modbus Events
In Modbus Slave Mode, the DMS-3K can send time stamped event data to a single Modbus
Master device.
In Modbus Master Mode, the DMS-3K can send time stamped event data to a single Modbus
Slave device.
Systems with CR (Combined Rack) option
When multiple racks are combined to form a system (option CR), the Master DMS-3K rack
(rack with option CR enabled) will have the capability to transmit the 'Modbus Events' for the
entire system from the one Master rack whether configured as a Modbus Slave or Modbus
Master.
For 'Modbus Alarms', the Master DMS-3K rack can transmit the alarm status for as many
alarms as will fit in the available registers. (see below)
Modbus
Communications
Mode
Mode
Master
Serial
Master
Ethernet
Slave
Serial or Ethernet
Notes:
Multiple inputs can be grouped together for a single Modbus bit to expand the
quantity of inputs. Example: DMS inputs 1 thru 5 can trigger a single Modbus bit.
Serial and Ethernet communications can be used simultaneously, each with their
own group of inputs to extend the total quantity of Modbus Outputs.
# of devices we can
transmit alarms to
Up to 6 Slave devices
Up to 8 Slave devices
One Master Device
# of
Total # of inputs
alarms/Device
Transmitted
128
768
128
1,024
128
128
Page 167
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