User Manual

APPENDIX USER’S MANUAL SWEEP V1.0

Performing Data Block Checksum

The last byte of a Data Block receipt is a checksum byte. It represents the sum of all bytes up until the checksum

byte (ie: the first 6 bytes). Obviously, a single byte caps at 255, so the checksum can't reliably hold the sum of 6

other bytes. Instead, the checksum byte uses the modulo operation and effectively contains the remainder after

dividing the sum by 255 (this is the same as saying sum % 255). Validating the checksum looks like:

//ONLY applies to receipts of type ReceiptEnum.DATA_BLOCK

//calculate the sum of the specified status or msg bytes

let calculatedSum = 0;

for(let i = 0; i < 6; i++){

//add each status byte to the running sum

calculatedSum += dataBlock[i];

}

calculatedSum = calculatedSum % 255;

let expectedSumVal = dataBlock[6];

return calculatedSum === expectedSumVal;