Warning
This README is a work-in-progress and may contain incomplete information or errors, however, the library itself is functional.
This is a library for managing Modbus RTU and TCP appication data units (ADUs). It is intended to be used with other libraries, but it can be used on its own.
Creating an instance of ModbusADU creates a structure with essentially the following form:
| Field | Length | Description |
|---|---|---|
| Transaction Identifier | 2 Bytes | Identification of a Modbus request |
| Protocol Identifier | 2 Bytes | 0 = Modbus protocol |
| Length | 2 Bytes | Number of following bytes, excluding error check |
| Unit Itentifier | 1 Byte | Identification of a remote slave/server device |
| Function Code | 1 Byte | Function of message: read, write, other |
| Data | 1 - 252 Bytes | Contents depend on function code |
| Error Check | 2 Bytes | Cyclic redundancy check (CRC) code |
This structure can be accessed as any of 4 byte-type arrays:
| Array | First Field |
|---|---|
| rtu | Unit Identifier |
| tcp | Transaction Identifier |
| pdu | Function Code |
| data | Data |
It can also be accessesd using the following methods:
- setTransactionId()
- setProtocolId()
- setLength()
- setUnitId();
- setFunctionCode();
- setDataRegister();