Modbus is a request/reply protocol that has one Modbus client in its network and may have many Modbus servers. Servers can control only their own internal states and clients can read and write data in them. Modbus is not restricted by the network type, in theory it can use any QIODevice. However, not every plugin supports all classes derived from QIODevice.
Each Modbus server has four tables in which it can store data.
| name | data range in one field | permissions for client |
|---|---|---|
| Discrete Inputs | 0-1 | Read |
| Coils | 0-1 | Read/Write |
| Input Registers | 0-65535 (0xffff) | Read |
| Holding Registers | 0-65535 (0xffff) | Read/Write |
The Modbus API provides some common API to access the Modbus devices:
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