The CHECKSUM step reads a checksum and compares it to the checksum calculated from the message contents. If the values differ, the reception of this message is aborted and a communication fault is reported.
The parameters of this step specifier are:
| SUM8 | Expects a one byte checksum done by adding all bytes and truncating the sum to the lowest 8 bits. |
| SUM8H | Like SUM8, but expects the checksum coded as a 2 digit hex number. |
| NSUM8 | Expects a one byte checksum done by adding all bytes, taking the negative value of the sum and then truncating the sum to the lowest 8 bits. |
| NSUM8H | Like NSUM8, but expects the checksum coded as a 2 digit hex number. |
| XOR8 | Expects a one byte checksum, done by XOR-ing all specified bytes. |
| XOR8H | Like XOR8, but expects the checksum coded as a 2 digit hex number. |
| MOD95 | Expects the one character 'modulo 95' checksum, known from the protocol used by Miteq devices (see below). |
| CRC8 | Expects a one byte CRC8 checksum. |
| CRC16L | Expects a two byte CRC16 checksum, calculated with the ARC/LHA CRC algorithm. Expects the least significant byte first (little endian). |
| CRC16B | Expects a two byte CRC16 checksum, calculated with the ARC/LHA CRC algorithm. Expects the most significant byte first (big endian). |
| start | The buffer position of the first character to be included in the checksum computation (0 means the first character). |
| end | The buffer position of the last character to be included in the checksum computation, relative to the actual position (-1 means the last character read). |
| offs | The buffer position where the checksum starts, relative to the actual position (-1 means the last character read). |
The MOD95 type checksum is computed following the formula:
