Module modbus 

Modbus protocol layer implementation.

Implements Modbus/TCP (MBAP), Modbus RTU, and Modbus ASCII frame formats.

Modbus/TCP (MBAP) Header Format

Offset  Size  Field
0       2     Transaction ID (big-endian)
2       2     Protocol ID (0x0000 for Modbus)
4       2     Length (number of following bytes, including Unit ID)
6       1     Unit ID (slave address)
7       1     Function Code
8..N    var   Data (function-code dependent)

Modbus RTU Frame Format

Offset  Size  Field
0       1     Slave Address
1       1     Function Code
2..N-2  var   Data
N-2     2     CRC-16 (little-endian)

Modbus ASCII Frame Format

':'  + hex(SlaveAddr + FuncCode + Data + LRC) + CR + LF

Re-exports

pub use builder::ModbusBuilder;

pub use crc::modbus_crc16;

pub use crc::modbus_lrc;

pub use crc::verify_crc16;

pub use crc::verify_lrc;

Modules

builder

Modbus packet builder.

crc

Modbus CRC-16 and LRC checksum functions.

except_code

Modbus exception code constants.

func_code

Modbus function code constants.

Structs

ModbusLayer

Modbus layer – a zero-copy view into a packet buffer.

Enums

ModbusFrameType

Modbus frame type.

Constants

MODBUS_MBAP_HEADER_LEN

MBAP header length (transId + protoId + length + unitId = 7 bytes).

MODBUS_MIN_HEADER_LEN

Minimum Modbus/TCP message: MBAP header (7) + function code (1) = 8 bytes.

MODBUS_TCP_PORT

Modbus/TCP default port.

Statics

MODBUS_FIELD_NAMES

Field names exported for Python/generic access.

Functions

except_code_name

Return a human-readable name for a Modbus exception code.

func_code_name

Return a human-readable name for a Modbus function code.

is_modbus_tcp_payload

Check if a TCP payload looks like a Modbus/TCP (MBAP) message.