After the bit flow sequence for the synchronization of reception, the frame byte contains the protocol data and direction identity.
| Frame byte | Binary Data | Definition |
| E0 | 1110 0000 | Command from master, no reply required, first transmission |
| E1 | 1110 0001 | Command from master, no reply required, repeated transmission |
| E2 | 1110 0010 | Command from master, reply required, first transmission |
| E3 | 1110 0011 | Command from master, reply required, repeated transmission |
| E4 | 1110 0100 | Reply from slave, ok, no errors found |
| E5 | 1110 0101 | Reply from slave, command not supported |
| E6 | 1110 0110 | Reply from slave, Parity error, repeat requested |
| E7 | 1110 0111 | Reply from slave, Command not recognized, repeat necessary |