title: Calculating checksum or XOR operations
body: <p>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. </p>
  
  <p>The sample string is: &amp;AHELLO N-12345\71 </p>
  
  <p>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. </p>
  
  <p><strong>How can you obtain 71 from "AHELLO N-12345"?</strong></p>
  
  <p>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.</p>
  
  <p>The text below is copied from the supplied literature and describes the "71" (ckck) in question...</p>
  
  <p><em>- 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".</em></p>