Testcode to read/write data on a DS1961 SHA-1 iButton
Commands to query the ibutton over the serial connection:
Poll for found iButton id numbers
Write the 16 hex-digit secret to the iButton
Do an authenticated read with the 6 hex-digits as 3-byte challenge Prints the data (all zero currently) and the 160-bit MAC, which is computed from the data, ibutton id, ibutton secret and challenge code.