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I'm using hyperterminal and trying to send strings a to 6 digit scoreboard. I was sent a sample string from the manufacturer to test with and it worked, but to be able change the displayed message I was told to calculate a new Checksum value.

The sample string is: &AHELLO N-12345\71

Charactors A and N are addresses for the scoreboards(allowing two displays be used through one RS232 connection). HELLO and -12345 are the characters to be shown on the display. The "71" is where I am getting stuck.

How can you obtain 71 from "AHELLO N-12345"?

In the literature supplied with the scoreboard, the "71" from the sample string is described as a character by character logical XOR operation on characters "AHELLO N-12345". The manufacturer however called it a checksum. I'm not trained in this type of language and I did try to research but I can't put it together on my own.

The text below is copied from the supplied literature and describes the "71" (ckck) in question...

- ckck = 2 ASCII control characters: corresponds to the two hexadecimal digits obtained by performing the character by character logical XOR operation on characters "AxxxxxxByyyyyy". If there is an error in these characters, the string is ignored Example: if the byte by byte logical XOR operation carried out on the ASCII codes of the characters of the "AxxxxxxByyyyyy" string returns the hexadecimal value 0x2A, the control characters ckck are "2" and "A".

HeresJeff
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1 Answers1

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You don't specify a language but here's the algorithm in C#. Basically xor the values of the string all together and you'll end up with a value of 113, 71 in hex. Hence 71 is on the end of the input string.

        string input = "AHELLO N-12345";

        UInt16 chk = 0;
        foreach(char ch in input) {
            chk ^= ch;
        }
        MessageBox.Show("value is " + chk);

Outputs "value is 113"

Richard Nixon
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