Checksum Calculation Program
 REM - This sample BASIC program converts the checksum value "sum" into the REM - three characters which are sent as part of the TAP protocol. The variables REM - d1, d2, and d3 contain the three digits which are to be added to the REM - transmitted data block. "INT" is the integer function which returns the REM - integer portion of a number. This function is required if the variables REM - are floating point numbers. If they are declared as integers then the INT REM - function is not required. This BASIC program may easily be converted to REM - other programming languages. REM - sum = 379 REM - Following the checksum example in the TAP Specification Document: REM - 1 2 3 A B C the checksum value is 379. REM - The following code will create the three characters to be transmitted REM - in order to represent this checksum. REM - d3 = 48+sum-INT(sum/16)*16 sum = INT(sum/16) d2 = 48+sum-INT(sum/16)*16 sum = INT(sum/16) d1 = 48+sum-INT(sum/16)*16 REM - REM - Print the three character checksum in decimal and ASCII REM - PRINT "d1="; d1, "d2="; d2, "d3="; d3 PRINT "d1\$="; CHR\$(d1), "d2\$="; CHR\$(d2), "d3\$="; CHR\$(d3)
 More Checksum Help
 The following is a message from: Dave Opdahl Like many of your other visitors I found your site quite useful. Your hard work hasn't gone unappreciated. I made use of your TAP protocol page and wanted to give a little back. Here is a checksum routine in C++ that I wrote. Feel free to put it up on your site. The checksum is a little confusing as described in the specification, I did notice that recently you put up a BASIC example. The code below may not be extremely portable, but it may help some people out. Keep up the good work! ``` //nChecksum is sum of all appropriate bytes in message //csTemp is just a string that gets filled with the 3 checksum bytes void CV3Page::CalcChecksumString(CString &csTemp, int nChecksum) { BYTE nFirstChar, nSecondChar, nThirdChar; int nTemp; //Calculate the checksum values nThirdChar = (BYTE)(nChecksum & 0x000F);//LS 4 bits nSecondChar = (BYTE)(nChecksum & 0x00F0);//MS 4 bits of LowByte nSecondChar >>= 4; nTemp = nChecksum & 0x0F00; //LS 4 bits of Hibyte nFirstChar = (BYTE)(nTemp >> 8); //Build up the checksum string... csTemp += (BYTE)(nFirstChar + 0x30); csTemp += (BYTE)(nSecondChar + 0x30); csTemp += (BYTE)(nThirdChar + 0x30); } ```

 END OF CHECKSUM HELP SECTION

 Home Page Directory Consulting Newsletters Free Subscription Products Reference Glossary Send e-mail