Modbus Master RTU Option

The Modbus Master Option enables the DiaLog Elite to read input values from a PLC, or other Modbus Slave device, and write relay control values. The connection to the PLC uses the RS-232/RS-485 serial connector on the Elite. The protocol is Modbus RTU, where the Elite is the Master and the PLC is the slave.

The option supports a combination of up to 72 total I/O channels – up to 48 of which can be physical I/O in the Elite.

The I/O read from the PLC can be any combination of analog (holding registers) or digital points (coils).

Values that are read from the PLC are interpreted by the Elite the same as if they were physical I/O in the Elite. All the alarm and control logic within the Elite operate on data coming from PLC registers.


  • PLC must support Modbus RTU support over a serial link.
  • Serial cable to link the Elite to the PLC.


  • Monitor Modbus communication link and alarm on loss of communication.
  • Any combination of up to 72 PLC analog, digital or relay points.
  • Any combination of physical points in the Elite.
  • Dial-in voice-based status of all channels.
  • Configuration through voice-based prompts either locally or remotely.
  • Supports faxing of status report on periodic or alarm basis providing immediate information on all channels.
  • Elite can be a Modbus Master and Modbus Slave concurrently for interface to SCADA.
  • Special display screens to view PLC channel status.
  • Programmable locally via keypad or PC.