Changes

The [[Vortex Disc Drives|Vortex disc interface]] uses other ports. See its dedicated wiki page.

== IC Models used in CPC ==

The CPC464, CPC472, 464 Plus and GX4000 are not equipped with a FDC chip.

== Accessing the FDC 765 ==

The Main Status Register signalizes when the FDC is ready to send/receive the next byte through the Data Register.

== FDC Command Table ==

Seek/Recalib: All read/write commands will be disabled until succesful senseint

Senseint: Set's IC if unsuccesful (no int has occured) (until IC=0)

== FDC Status Registers ==

b6 WP Write Protected (write protected)

b7 FT Fault (if supported: 1=Drive failure)

== Motor On/Off Flipflop ==

An exception are the Vortex F1-S, F1-D, M1-S and M1-D drives. (How are they different?)

== Unconnected Pins ==

In the CPC the US1 signal of the FDC is not connected, making it impossible to select floppy drives 2 and 3. The floppy drives 0 and 1 are selected instead.

== Ready / Disk Changed signal ==

Other solutions exist to [[Modify PC floppy drives]] to recreate a Ready signal. Also, Gotek drives (with a FlashFloppy or HxC firmware) can be configured to simulate the Ready signal.

== Notes ==

Usually single sided 40-track 3" disk drives are used in CPCs. For practical purposes, 42 tracks could be used — the limit is specific to the drive and some support more tracks but 42 is a good maximum. The FDC controller can be used to control 80-tracks and/or double sided drives, though AMSDOS doesn't support such formats. AMSDOS supports a maximum of two disk drives only.

== FDC Track Format ==

[[File:FDC765 Track Format.png]]

== Internal details of the chip ==

* From [https://hackaday.com/2012/08/13/taking-a-look-at-decapped-ics/#comment-734991 a comment in the hackaday website]: "Internally this is a microcoded part with a primative controller of NEC’s own design. Testing microcode embedded in a part can be troublesome. The uPD765 had a few extra gates associated with the DMA Request and DMA Ack pins. Presenting a certain illegal combination here places the part into a “test” mode and allows the sequencer microcode to be output on the normal Data pins. The sequencer microcode is responsible for high level commands such as Read Track, Recalibrate, Format Track, or Write Data. There is a similar test mode for the nano-code array which serializes data at the floppy disk head."

== FDC Block Diagram ==

[[File:FDC Intel 8272A block diagram.gif]]

== Generic System Diagram ==

[[File:UPD765A System Diagram.png]]

== PC to CPC floppy connector ==

[[File:Cpc6128floppytopcfloppy.gif]]

== FDD Block Diagram ==

[[File:Floppy Disk Drive - Block Diagram.png]]

== Datasheets ==

* [[Media:Panasonic-3 inch Floppy Drive EME-150.pdf]] Panasonic EME-150M 3inch Floppy Disk Drive Datasheet

* [[Media:NEC_FD1035_Floppy.pdf]] - NEC FD1035 3.5inch Floppy Disk Drive Datasheet (1984)

== External links ==