MODBUS is one of the most widely used communication protocols in industrial automation. inSCADA supports multiple variants of the MODBUS protocol in both Client (Master) and Server (Slave) roles.
Each MODBUS connection in inSCADA is defined in the following hierarchical structure:
└── Device (identified by Slave ID)
└── Frame (Register block)
└── Variable (Single register/bit address)
Common connection parameters for all MODBUS variants:
Parameter Type Description IP / Host String Target device IP address or hostname Port Integer Target port (default: 502) Timeout Integer (ms) Response wait time Connect Timeout Integer (ms) Connection establishment timeout Retries Integer Failed request retry count Pool Size Integer Connection pool size Max Idle Timeout Integer (ms) Idle connection timeout Check CRC Boolean CRC validation check (for RTU) Reconnect on Error Boolean Automatic reconnection on error
Parameter Type Description Station Address Integer (1-247) MODBUS Slave address (Unit ID) Scan Time Integer (ms) Scan period Scan Type Enum PERIODIC or FIXED_DELAYRetain Flag Boolean Retain last value
Parameter Type Description Type Enum Register type (see below) Start Address Integer Starting register address Quantity Integer Number of registers to read Inter Frame Delay Integer (ms) Delay between frames Is Readable Boolean Read permission Is Writable Boolean Write permission Minutes Offset Integer Time offset (minutes) Scan Time Factor Integer Scan multiplier
Type Function Code Read Write Description Coil FC01 / FC05 / FC15 ✓ ✓ Digital output (1 bit) Discrete Input FC02 ✓ — Digital input (1 bit, read-only) Holding Register FC03 / FC06 / FC16 ✓ ✓ Analog output (16 bit) Input Register FC04 ✓ — Analog input (16 bit, read-only)
Parameter Type Description Start Address Integer Register address (offset within frame) Type Enum Data type (see below) Byte Swap Boolean Byte order swap (Big/Little Endian) Word Swap Boolean Word order swap (for 32-bit values) Bit Offset Integer Bit address (for Coil/Discrete) Length Integer Character length for String type
Data Type Size Description Boolean 1 bit Single bit value Byte 8 bit Signed byte Unsigned Byte 8 bit Unsigned byte Short 16 bit Signed 16-bit integer Unsigned Short 16 bit Unsigned 16-bit integer Integer 32 bit Signed 32-bit integer Unsigned Integer 32 bit Unsigned 32-bit integer Long 64 bit Signed 64-bit integer Float 32 bit IEEE 754 floating point Double 64 bit IEEE 754 double precision 16 BIT BCD 16 bit Binary Coded Decimal 32 BIT BCD 32 bit Binary Coded Decimal 64 BIT BCD 64 bit Binary Coded Decimal String Variable ASCII character string
For variant-specific configuration details:
