![]() In VB.Net and C# you can use the ToString function for this, e.g. ![]() ![]() What is left is to transform the checksum into two hexadecimal characters, and that is it. In Java script:įor(var i = 0 i < stringToCalculateTheChecksumOver.length i++) In VB.Net:įor Each Character As Char In stringToCalculateTheChecksumOverĬhecksum = checksum Xor Convert.ToByte(Character) Then just XOR the first character with the next character, until the end of the string.īelow you find a code example in Java script, VB.Net and C#. In the examples below the name of this new string is stringToCalculateTheChecksumOver. To calculate the checksum you parse all characters between $ and * from the NMEA sentence into a new string. The string that the checksum is calculated over is In this sentence the checksum is the character representation of the hexadecimal value 28. To calculate a checksum for a NMEA0183 which doesnt contain a checksum field already. It is the representation of two hexadecimal characters of an XOR of all characters in the sentence between – but not including – the $ and the * character. ![]() Yet, since it is better than having no method at all for validating, I do recommend to always transmit a valid checksum and to always check the validity of the checksum of received sentences.Ĭalculating the checksum is very easy. Instruments do transmit a continuous stream of sentences and the data is normally refreshed every second or faster so you get a retransmit anyway, although with slightly modified data of course.There is no standard method in the NMEA protocol defined to ask for a retransmission in case of an invalid checksum.The checksum algorithm used is not a very reliable method of checking for transmission errors or invalidating the received data.Some manufacturers (and software developers…) do not bother too much when it comes to the checksum in NMEA sentences. ![]()
0 Comments
Leave a Reply. |