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- byte 1 is meaningful only for SYS8X00 and serial Modbus
- byte 3 is meaningful only for E642 and EEI
- byte 0 and byte 2 do not depend on "protocol" and are passed through as they are.
Be aware that byte that byte 1 and byte 3 can still also be used to discriminate other classes (besides those mentioned above) but, in that case, they have to be interpreted by appropriate a dedicated piece of code.
00 01 01 01
| 3 | 2 | 1 | 0 |
byte 3 type 1,5A,5B
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