alicat_basis2_modbus.hpp File Reference

Modbus-RTU framing and CRC-16 helpers used by the BASIS-2 driver. More...

#include <array>
#include <cstdint>
#include <cstddef>
#include "alicat_basis2_registers.hpp"
#include "alicat_basis2_types.hpp"

Include dependency graph for alicat_basis2_modbus.hpp:

This graph shows which files directly or indirectly include this file:

Go to the source code of this file.

Namespaces
namespace	alicat_basis2
namespace	alicat_basis2::modbus

Functions
uint16_t	alicat_basis2::modbus::Crc16 (const uint8_t *data, std::size_t length) noexcept
	Compute the Modbus-RTU CRC-16 over a byte buffer.
std::size_t	alicat_basis2::modbus::AppendCrc (uint8_t *frame, std::size_t length) noexcept
	Append the CRC-16 to frame[length..length+1] and return new length.
bool	alicat_basis2::modbus::CheckCrc (const uint8_t *frame, std::size_t length) noexcept
	Verify the CRC at frame[length-2..length-1] matches the body.
std::size_t	alicat_basis2::modbus::BuildReadHolding (uint8_t unit_addr, uint16_t reg_addr, uint16_t reg_count, uint8_t *out, std::size_t out_capacity) noexcept
	Build a Function-03 (Read Holding Registers) request.
std::size_t	alicat_basis2::modbus::BuildWriteSingle (uint8_t unit_addr, uint16_t reg_addr, uint16_t value, uint8_t *out, std::size_t out_capacity) noexcept
	Build a Function-06 (Write Single Register) request.
std::size_t	alicat_basis2::modbus::BuildWriteMultiple (uint8_t unit_addr, uint16_t reg_addr, const uint16_t *regs, uint8_t count, uint8_t *out, std::size_t out_capacity) noexcept
	Build a Function-16 (Write Multiple Registers) request.
constexpr uint32_t	alicat_basis2::modbus::InterFrameGapUs (uint32_t bps) noexcept
	Minimum idle time t3.5 between two Modbus-RTU frames, in microseconds.
constexpr uint32_t	alicat_basis2::modbus::InterFrameGapMs (uint32_t bps) noexcept
	InterFrameGapUs(bps) rounded up to whole milliseconds (for UartInterface::delay_ms()).
bool	alicat_basis2::modbus::IsExceptionReply (const uint8_t *frame, std::size_t length) noexcept
DriverError	alicat_basis2::modbus::ParseException (const uint8_t *frame, std::size_t length, uint8_t expected_addr, uint8_t expected_fn, uint8_t *code) noexcept
	Parse a 5-byte exception reply (Modbus Application Protocol V1.1b3, section 7).
DriverError	alicat_basis2::modbus::ParseReadHolding (const uint8_t *frame, std::size_t length, uint8_t expected_addr, uint8_t expected_count, uint16_t *regs) noexcept
	Parse a Function-03 response into regs[].
DriverError	alicat_basis2::modbus::ParseWriteSingleEcho (const uint8_t *frame, std::size_t length, const uint8_t *request, std::size_t req_len) noexcept
	Validate the echo of a Function-06 (Write Single) request against the just-sent request.
DriverError	alicat_basis2::modbus::ParseWriteMultipleEcho (const uint8_t *frame, std::size_t length, uint8_t expected_addr, uint16_t expected_reg_addr, uint16_t expected_count) noexcept
	Validate the response of a Function-16 (Write Multiple) request.

Variables
constexpr uint32_t	alicat_basis2::modbus::kRtuBitsPerChar = 11
	Bits per RTU character used for the timing: start + 8 data + parity/stop + stop (section 2.5.1).
constexpr uint32_t	alicat_basis2::modbus::kFixedGapAboveBps = 19200
	Above this baud rate the spec fixes t3.5 at 1750 us instead of 3.5 character times.
constexpr uint32_t	alicat_basis2::modbus::kFixedGapUs = 1750
	The fixed t3.5 used above 19200 baud, in microseconds.
constexpr std::size_t	alicat_basis2::modbus::kExceptionFrameLength = 5
	Length of a Modbus-RTU exception reply: address, function | 0x80, exception code, CRC-16.
constexpr std::size_t	alicat_basis2::modbus::kReplyHeaderLength = 3
	Number of reply bytes a receiver reads before it can tell an exception reply (bit 7 of the function code set) from a normal one: address, function code, and one more byte.

Detailed Description

Modbus-RTU framing and CRC-16 helpers used by the BASIS-2 driver.

Implements only the three function codes BASIS-2 supports: 03 — Read Holding Registers 06 — Write Single Register 16 — Write Multiple Registers plus the canonical Modbus CRC-16 (polynomial 0xA001, init 0xFFFF, LSB first) defined by the Modbus-RTU specification.

All routines are pure / constexpr-friendly, allocation-free, and operate on plain uint8_t* byte buffers so the implementation can be reused on any MCU without the STL.

Copyright

Copyright (c) 2026 HardFOC. All rights reserved.