Introduction
The SKE4 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 SKE4 devices.
The SKE4 Modbus Guide assumes that you are familiar with Modbus terminology.
The following are the requirements for Modbus:
Data Model. The SKE4 Steam Humidifier Modbus server data model uses only the Modbus Registers table.
Register Address:
oAs per protocol base (base 0); for PLC add 1 to protocol base.
oAs per holding register (base 400001).
Function Codes. The SKE4 Steam Humidifier Modbus server supports a limited function codes subset
comprising:
oRead Holding Registers (0x03)
oWrite Single Register (0x06)
oWrite Multiple Registers (0x10)
Exception Responses. The SKE4 Steam Humidifier Modbus server supports the following exception codes:
oIllegal data address
oIllegal data value
oSlave device busy
Serial Line. The SKE4 Steam Humidifier Modbus over serial line uses RTU transmission mode over a two-wire
configuration RS485 (EIA/TIA-485 standard) physical layer.
oThe 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.
oThe supported baud rates are 9600, 19200, 38400, and 57600.
oThe 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.
oIn 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 SKE4 Steam Humidifier device only answers at the following address:
oThe device's unique address (1 to 246) that can be set through the device menu or through holding
register index 0.
