Modbus
Modbus is a communication protocol utilized in PLC networks. Originally developed for serial interfaces like RS232, RS422, and RS485, it was later expanded to include TCP mode. OIBus uses the jsmodbus library in TCP mode only.
Specific Settings
Connection Configuration
| Setting | Description | Example Value |
|---|---|---|
| Host | IP address or hostname of the Modbus server machine. | 192.168.1.100 |
| Port | Port to use for connection (502 by default). | 502 |
| Connection timeout | Maximum time to wait for a connection (in milliseconds). | 10000 |
| Retry interval | Time to wait (in milliseconds) between reconnections after a connection failure. | 5000 |
| Slave ID | Identifies the Modbus source machine (default is 1). | 1 |
| Address offset | For most PLCs, there is no offset (Modbus option). Some PLCs may start the address range at 1 instead of 0 (JBus option) | Modbus |
Data Format Options
| Setting | Description | |
|---|---|---|
| Endianness | Specifies the type of bit encoding (Big Endian or Little Endian). | Big Endian |
| Swap Bytes | Determines whether the bytes within a group of 16 bits (a word) should be inverted or not. | Enabled/Disabled |
| Swap Words | Indicates whether the words (16-bit groups) should be inverted or not within a 32-bit group. | Enabled/Disabled |
Item Settings
| Setting | Description | Example Value |
|---|---|---|
| Address | Hexadecimal address of the data within the device (without the data type digit). | 0x0001 |
| Modbus type | Specifies whether it's a coil, discrete input, input register, or holding register (default). | Holding Register |
| Data type | Relevant for holding registers or input registers. Defines the type of data fetched from the register (Bit, UInt16, Int16, UInt32, Int32, UInt64, Int64, Float, Double). | UInt16 |
| Bit index | (Bit data type only) The index of the bit to retrieve from the read value (0 to 15). | 0 to 15 |
| Multiplier Coefficient | Multiplies the retrieved value (default is 1). | 1 |
About Modbus Addresses
The address should match the variable's address in the PLC, represented in hexadecimal without the data type digit.
Examples:
- For holding register data at 0x40001, input the address as 0x0001 and specify the Modbus type as holdingRegister
- For coil data at 0x009C, use 0x009C as the address and specify the Modbus type as coil
Address Ranges (Modicon Convention Notation):
| Type | Standard Range | Extended Range |
|---|---|---|
| Coil | 0x00001 - 0x09999 | 0x000001 - 0x065535 |
| Discrete Input | 0x10001 - 0x19999 | 0x100001 - 0x165535 |
| Input Register | 0x30001 - 0x39999 | 0x300001 - 0x365535 |
| Holding Register | 0x40001 - 0x49999 | 0x400001 - 0x465535 |
For more details, see the Modicon Convention Notation (MCN).