Question

I’m sending a byte array to a piece of hardware.

The first 7 bytes contain data and the 8th byte is a checksum.

The 8th byte is the Least Significant Byte of the sum of the first 7 bytes.

Examples that include the correct checksum. The last byte of each of these is the checksum

200-30-7-5-1-2-0-245

42-0-0-1-176-0-148-39

42-0-0-3-177-0-201-118

How do I calculate the checksum?

Thanks,
Seth

Answer 1

Same as in C: take the sum and ‘bitwise and’ it with 255 (or 0xff in hexadecimal). Using your first set of data as an example:

arr = [ 200, 30, 7, 5, 1, 2, 0 ]

sum = 0
arr.each do |val|
    sum += val
end
checksum = sum & 0xff

print checksum