Sml.CRC16 (SmlEx v0.1.0)

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The 16 bit checksums used by SML for the transport frame and each message.

The standard algorithm is CRC-16/X-25 (polynomial 0x1021 reflected, init 0xFFFF, final XOR 0xFFFF), transmitted low byte first. Some meters, notably the Holley DTZ541, use CRC-16/Kermit (init 0, no final XOR) transmitted high byte first instead.

valid?/3 checks the two checksum bytes as they appear on the wire against either or both variants.

Summary

Types

mode()

Functions

kermit(data)

Calculates the CRC-16/Kermit checksum of data.

valid?(data, crc, atom)

Checks the checksum bytes crc (in wire order) for data.

x25(data)

Calculates the CRC-16/X-25 checksum of data.

Types

mode()

@type mode() :: :auto | :x25 | :kermit

Functions

kermit(data)

@spec kermit(binary()) :: 0..65535

Calculates the CRC-16/Kermit checksum of data.

iex> Sml.CRC16.kermit("123456789")
0x2189

valid?(data, crc, atom)

@spec valid?(binary(), <<_::16>>, mode()) :: boolean()

Checks the checksum bytes crc (in wire order) for data.

mode is :x25, :kermit or :auto (accept either).

iex> Sml.CRC16.valid?("123456789", <<0x6E, 0x90>>, :x25)
true

iex> Sml.CRC16.valid?("123456789", <<0x21, 0x89>>, :auto)
true

x25(data)

@spec x25(binary()) :: 0..65535

Calculates the CRC-16/X-25 checksum of data.

iex> Sml.CRC16.x25("123456789")
0x906E