User Guide

SKVF Evaporative Cooler
Modbus Communication Module User Guide
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Introduction
The SKVF Modbus Communication Module User Guide provides information for using Neptronic
®
communication
feature. The controller uses Modbus communication protocol over serial line in the RTU mode and provides a Modbus
network interface between client devices and Neptronic SKVF devices.
The SKVF Modbus Guide assumes that you are familiar with Modbus terminology.
The following are the requirements for Modbus:
• Data Model. The Evaporative Cooler Modbus server data model uses only the Modbus Registers table.
• Register Address:
o As per protocol base (base 0); for PLC add 1 to protocol base.
o As per holding register (base 400001).
Note: Ensure that the Modbus communication software used does not have a limit on the range of the
register addresses that can be viewed and supports 6-digit holding registers.
• Function Codes. The Evaporative Cooler Modbus server supports a limited function codes subset comprising:
o Read Holding Registers (0x03)
o Write Single Register (0x06)
o Write Multiple Registers (0x10)
• Exception Responses. The Evaporative Cooler Modbus server supports the following exception codes:
o Illegal data address
o Illegal data value
o Slave device busy
• Serial Line. The Evaporative Cooler Modbus over serial line uses RTU transmission mode over a two-wire
configuration RS485 (EIA/TIA-485 standard) physical layer.
o The physical layer can use fixed baud rate selection or automatic baud rate detection (default) as per
the Modbus Auto Baud Rate device menu item or holding register index 1.
o The supported baud rates are 9600, 19200, 38400, and 57600.
o The physical layer also supports variable parity control and stop bit configuration as per the Modbus
Comport Config device menu item or holding register index 2.
o In auto baud rate configuration, if the device detects only consecutive bad frames (2 or more) for one
second with any given baud rate, it will reinitialize itself to the next baud rate.
• Addressing. The Evaporative Cooler device only answers at the following address:
o The device's unique address (1 to 246) that can be set through the device menu or through holding
register index 0.