Enum FunctionCode 

#[repr(u8)]
pub enum FunctionCode {
    Default = 0,
    ReadCoils = 1,
    ReadDiscreteInputs = 2,
    WriteSingleCoil = 5,
    WriteMultipleCoils = 15,
    ReadHoldingRegisters = 3,
    ReadInputRegisters = 4,
    WriteSingleRegister = 6,
    WriteMultipleRegisters = 16,
    MaskWriteRegister = 22,
    ReadWriteMultipleRegisters = 23,
    ReadFifoQueue = 24,
    ReadFileRecord = 20,
    WriteFileRecord = 21,
    ReadExceptionStatus = 7,
    Diagnostics = 8,
    GetCommEventCounter = 11,
    GetCommEventLog = 12,
    ReportServerId = 17,
    EncapsulatedInterfaceTransport = 43,
}

Modbus Public Function Codes.

These are the standardized function codes defined in the Modbus Application Protocol Specification V1.1b3.

See:

• Section 5.1 Public Function Code Definition
• Section 6.x for individual function behaviors

Reference: :contentReference[oaicite:1]{index=1}

Variants

Default = 0

0x00 — Undefined This value is not defined in the specification and can be used as a placeholder for uninitialized or unknown function codes. It is not a valid function code for actual Modbus transactions.

ReadCoils = 1

0x01 — Read Coils

Reads the ON/OFF status of discrete output coils. Section 6.1

ReadDiscreteInputs = 2

0x02 — Read Discrete Inputs

Reads the ON/OFF status of discrete input contacts. Section 6.2

WriteSingleCoil = 5

0x05 — Write Single Coil

Forces a single coil to ON (0xFF00) or OFF (0x0000). Section 6.5

WriteMultipleCoils = 15

0x0F — Write Multiple Coils

Forces multiple coils to ON/OFF. Section 6.11

ReadHoldingRegisters = 3

0x03 — Read Holding Registers

Reads one or more 16-bit holding registers. Section 6.3

ReadInputRegisters = 4

0x04 — Read Input Registers

Reads one or more 16-bit input registers. Section 6.4

WriteSingleRegister = 6

0x06 — Write Single Register

Writes a single 16-bit holding register. Section 6.6

WriteMultipleRegisters = 16

0x10 — Write Multiple Registers

Writes multiple 16-bit holding registers. Section 6.12

MaskWriteRegister = 22

0x16 — Mask Write Register

Performs a bitwise mask write on a single register. Section 6.16

ReadWriteMultipleRegisters = 23

0x17 — Read/Write Multiple Registers

Reads and writes multiple registers in a single transaction. Section 6.17

ReadFifoQueue = 24

0x18 — Read FIFO Queue

Reads the contents of a FIFO queue. Section 6.18

ReadFileRecord = 20

0x14 — Read File Record

Reads structured file records. Section 6.14

WriteFileRecord = 21

0x15 — Write File Record

Writes structured file records. Section 6.15

ReadExceptionStatus = 7

0x07 — Read Exception Status (Serial Line Only)

Returns 8-bit exception status. Section 6.7

Diagnostics = 8

0x08 — Diagnostics (Serial Line Only)

Provides diagnostic and loopback tests. Requires sub-function codes. Section 6.8

GetCommEventCounter = 11

0x0B — Get Communication Event Counter (Serial Line Only)

Returns communication event counter. Section 6.9

GetCommEventLog = 12

0x0C — Get Communication Event Log (Serial Line Only)

Returns communication event log. Section 6.10

ReportServerId = 17

0x11 — Report Server ID (Serial Line Only)

Returns server identification. Section 6.13

EncapsulatedInterfaceTransport = 43

0x2B — Encapsulated Interface Transport

Used for:

• CANopen General Reference (Sub-function 0x0D)
• Read Device Identification (Sub-function 0x0E)

Section 6.19, 6.20, 6.21

Trait Implementations

impl Clone for FunctionCode

fn clone(&self) -> FunctionCode

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FunctionCode

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for FunctionCode

fn default() -> FunctionCode

Returns the “default value” for a type.

impl PartialEq for FunctionCode

fn eq(&self, other: &FunctionCode) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl TryFrom<u8> for FunctionCode

type Error = MbusError

The type returned in the event of a conversion error.

fn try_from(value: u8) -> Result<Self, Self::Error>

Performs the conversion.

impl Copy for FunctionCode

impl Eq for FunctionCode

impl StructuralPartialEq for FunctionCode