# modbus protocol auxiliary library

## Function

`modbus()` provides Modbus RTU/TCP frame construction, CRC16 checksum response parsing capabilities. It only handles protocol bytes and does not directly open a serial port or TCP connection.

## Syntax

```bt
modbus.method(args)
modbus().method(args)
```

## Parameters

 are determined according to the specific method.

## Return Value

 is determined by the specific method.

## Method

| Method | Description |
|------|------|
| [rtu_request](/en/docs/modbus/rtu_request) | Constructs a Modbus RTU request frame. |
| [tcp_request](/en/docs/modbus/tcp_request) | Construct a Modbus TCP request frame. |
| [parse_rtu](/en/docs/modbus/parse_rtu) | Parse Modbus RTU response frame. |
| [parse_tcp](/en/docs/modbus/parse_tcp) | Parse Modbus TCP response frames. |
| [crc16](/en/docs/modbus/crc16) | Calculate Modbus RTU CRC16. |

## Code Examples

```bt
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

- The generated request frame returns Bytes and can be passed directly to `serial.write()`, `tcp.write()` or `ws.send()`.
-Supported function names: `read_coils`, `read_discrete_inputs`, `read_holding_registers`, `read_input_registers`, `write_single_coil`, `write_single_register`, `write_multiple_coils`, `write_multiple_registers`.
- Pass in `pdu: bytes(...)` when you need to customize PDU.