# modbus.parse_rtu

## Function

Parse Modbus RTU response frames, check CRC and extract common response fields.

## Syntax

```bt
modbus.parse_rtu(data)
```

## Parameters

| Parameters | Type | Required | Default value | Description |
|------|------|------|------|------|
| data | Bytes/Array/String | Yes | None | RTU response frame. |

## Return value

| Type | Description |
|------|------|
| Object | Returns the RTU response parsing object. See "Return Object Fields" below for fields. |

## Return object fields

| Field | Type | Must exist | Description |
|------|------|------|------|
| protocol | String | Yes | Protocol type, fixed to `rtu`. |
| unit_id | Int | Yes | RTU slave address. |
| crc | Int | Yes | The CRC16 value carried at the end of the response frame, parsed with the low byte first. |
| crc_expected | Int | Yes | The CRC16 value recalculated based on the response payload. |
| valid_crc | Bool | Yes | Whether `crc` is equal to `crc_expected`. Parsing of the PDU continues even if the CRC does not match. |
| function_code | Int | Yes | Response function code. The exception response will have the highest bit, for example `0x83`. |
| exception | Bool | Yes | Whether it is a Modbus exception response. |
| exception_code | Int/Empty | No | The exception code of the exception response; only written when `exception` is `true`, and `empty` when the exception code is missing in the response. |
| data | Bytes | Yes | The original data in the PDU after removing the function code. The exception response contains exception code bytes. |
| byte_count | Int | No | Number of data bytes in the read coil, read discrete input, read holding register, read input register response. Other responses do not write this field. |
| coils | Array | No | Read coils or read a parsed Boolean array of discrete input responses. Other responses do not write this field. |
| registers | Array | No | Reading a holding register or reading an input register responds to a parsed 16-bit unsigned register integer array. Other responses do not write this field. |
| address | Int | No | Write single coil, write single register, write multiple coils, write multiple registers Confirm the starting address in the response. Other responses do not write this field. |
| value | Int | No | The quantity or value to write in the confirmation response. Function code 5/6 represents the written value, and function code 15/16 represents the written quantity. |

## Code Example

```bt
frame = bytes('010304000a0014da3e', 'hex')
result = modbus.parse_rtu(frame)

// Output: 10
print result.registers[0]
```

## Notes

- The data will not be discarded when the CRC does not match, `valid_crc` returns false, and the script can decide whether to discard it.
- Exception responses will return `exception: true` and `exception_code`.