Operations executed by the controller are divided into a command phase, an execution phase and a result phase.
During the command phase bytes are sent to the control registers and flags via the data in/out register.
Then the requested operation is performed during the execution phase and upon completion of the operation, theresult phase is entered and status information is read by the processor.
The outputs during the command phase and inputs during the result phase are performed using single-byte transfers, even though any data transfer that takes place in the execution phase is normally supervised by a DMA controller.


The possible 8272 commands are:

Read Data -Reads data from a data field on a diskette
Write Data -Writes data to a data field on a diskette
Read Deleted Data -Reads data from a field marked as being deleted.
Write Deleted Data -Writes a deleted data address mark and puts filler characters in the data field.
Read A Track -Reads an entire track of data fields.
Read ID -Reads the identification field.
Format A Track -Writes the formatting information to a track using program supplied formatting parameters.
Scan Equal..........................}
Scan Low or Equal..............} Scans the data for specified condition and makes an
Scan High or Equal.............} interrupt request when the condition is satisfied.
Recalibrate -Causes the head to be retracted to track 0.
Sense Interrupt Status -Reads status information from STO after interrupts caused by ready line changes and seek operations.
Specify -Sets the step rate , head unload time, head load time and DMA mode.
Sense Drive Status -Inputs the drive status from ST3.
Seek -Positions head over a specified track.