The ports used by Amstrad and compatible interfaces use:
* Port FA7Eh &FA7E - Floppy Motor On/Off Flipflop* Port FB7Eh &FB7E - FDC 765 Main Status Register (read only)* Port FB7Fh &FB7F - FDC 765 Data Register (read/write)
The [[Vortex Disc Drives|Vortex disc interface]] uses other ports. See its dedicated wiki page.
== Accessing the FDC 765 ==
The Main Status Register (Port FB7Eh&FB7E) signalizes when the FDC is ready to send/receive the next byte through the Data Register.
The Data Register (Port FB7Fh&FB7F) is used to write Commands and Parameters, to read/write data bytes, and to receive result bytes. These three operations are called Command-, Execution-, and Result-Phase.
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== FDC Status Registers ==
The Main Status register can be always read through Port &FB7E. The other four Status Registers cannot be read directly, instead they are returned through the data register as result bytes in response to specific commands.
Main Status Register (Port &FB7E):
b0..3 DB FDD0..3 Busy (seek/recalib active, until succesful sense intstat)
b7 RQM Request For Master (1=ready for next byte) (see b6 for direction)
Status Register 0:
b0,1 US Unit Select (driveno during interrupt)
or senseint with no int occured, 3=aborted:disc removed etc.)
Status Register 1:
b0 MA Missing Address Mark (Sector_ID or DAM not found)
b7 EN End of Track (set past most read/write commands) (see IC)
Status Register 2:
b0 MD Missing Address Mark in Data Field (DAM not found)
b7 0 Not Used
Status Register 3:
b0,1 US Unit Select (pin 28,29 of FDC)
== Motor On/Off Flipflop ==
Writing 00h to Port FA7Eh &FA7E turns all disk drive motors off, writing 01h turns all motors on. It is not possible to turn on/off the motor of a specific drive separately.
An exception are the Vortex F1-S, F1-D, M1-S and M1-D drives. (How are they different?)