Module protocol 

Defines data structures, constants, and protocol logic for interacting with an 8-Channel Multifunction RS485 Module via Modbus RTU, based on the protocol specification document.

This module covers:

• Representing port states (PortState, PortStates).
• Identifying specific ports (Port) and the Modbus device address (Address).
• Defining Modbus register addresses and data values for reading states and controlling ports.
• Encoding and decoding values from/to Modbus register format (Word).
• Error handling for invalid port or address values.

Assumes standard Modbus function codes “Read Holding Registers” (0x03) and “Write Single Register” (0x06) are used externally to interact with the device.

Structs

Address

Represents a validated Modbus device address, used for RTU communication over RS485.

ErrorAddressOutOfRange

Error indicating that a provided Modbus device address (u8) is outside the valid range for assignable addresses, defined by Address::MIN and Address::MAX (inclusive).

ErrorPortOutOfRange

Error indicating that a provided port index (u8) is outside the valid range defined by Port::MIN and Port::MAX (inclusive).

Port

Represents a validated port index, guaranteed to be within the valid range 0..NUMBER_OF_PORTS.

PortStates

Represents the collective states of all NUMBER_OF_PORTS ports.

PortsAll

A zero-sized type providing constants for controlling all ports simultaneously.

Enums

Error

A comprehensive error type for all operations within the protocol module.

PortState

Represents the state of a single digital I/O port (e.g., relay).

Constants

NUMBER_OF_PORTS

The total number of controllable digital I/O ports on the module.

Type Aliases

Word

Represents a single 16-bit value stored in a Modbus register.