ELK M1 Gold CheckSum Calculator

def calcElkCS(s):
  """
  Calculates checksum for sending commands to the ELKM1.
  Sums the ASCII character values mod256 and takes
  the lower byte of the two's complement of that value.
  """
  s = ('%02X' % (len(s) + 2)) + s
  cs = '%2X' % (-(sum(ord(c) for c in s) % 256) & 0xFF)
  return s+cs