modbus.tcp_request
modbus.tcp_request
Function
Construct Modbus TCP request frame, including MBAP header and PDU.
Syntax
modbus.tcp_request(config)
Parameters
| Parameters | Type | Required | Default value | Description |
|---|---|---|---|---|
| config | Object | Yes | None | Requests a configuration object. |
Configuration fields
| Field | Type | Required | Default value | Description |
|---|---|---|---|---|
| transaction_id | Int | No | 1 | TCP transaction number. |
| protocol_id | Int | No | 0 | Modbus TCP protocol number, usually 0. |
| unit_id | Int | No | 1 | Unit ID. |
| function_code/function/address/quantity/value/values/pdu/data | Same as rtu_request | Determined by function | None | PDU construction field. |
Return value
| Type | Description |
|---|---|
| Bytes | Modbus TCP ADU complete request frame. |
Code Example
packet = modbus.tcp_request({ transaction_id: 1, unit_id: 1, function: 'read_holding_registers', address: 0, quantity: 2 }) // Output: 000100000006010300000002 print packet.to_hex()
Notes
- MBAP length field is automatically written with
unit_id + pdulength.