The authentication procedure is described in the following steps:
- The host writes 0x00 to 0x3E.
- The host writes 0x00 to 0x3F.
- Write the random challenge should be written in a 32-byte block to address 0x40–0x5F.
- Write the checksum (1’s complement sum of (1), (2), and (3)) to address 0x60.
- Write the length 0x24 to address 0x61.
- The gauge will compute the HMAC using SHA-256 after step (5). Wait 200 ms. (60 ms is how long authentication takes, but extra margin is added).
- The MACData() command will contain the computed HMAC result using SHA-256.
- [AUTH] = 1 in OperationStatusB().