The sequence needed to complete four of these commands is given in Fig.9-49 as an example.The read data command includes all three phases, the seek command includes only the command and exe cution phases, the sense drive status command includes only the command and result phases and the specify command consists only of the command phase.

In all cases, the commands must be performed in their entirety (including the result phase, if applicable) or they will be considered incomplete. If an invalid command is given, the 8272 will return the status byte STO in response to the next input from the data in/out register.