Changes
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.
== 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.
[https://scarybeastsecurity.blogspot.com/2020/11/reverse-engineering-forgotten-1970s.html The decapped photos of Intel 8271, uPD765 and Intel 8272 chips] prove that uPD765 and Intel 8272 chips are identical.
== Datasheets ==
* [[Media:UPD765_App_Note_Mar79.pdf| NEC uPD765 Datasheet preliminary (1979)]] [[Media:UPD765 Datasheet OCRed.pdf]] [[Media:UPD765-NEC.pdf]] - uPD765 disc controller
* [https://www.threedee.com/jcm/terak/docs/Intel%208272A%20Floppy%20Controller.pdf Intel 8272A Datasheet preliminary (1982)] [[Media:Datasheet.hk_d8272a_2873060.pdf|Intel 8272A Datasheet (1986)]] - Identical clone Clone of the uPD765. [https://scarybeastsecurity.blogspot.com/2020/11/reverse-engineering-forgotten-1970s.html The decapped photos of both chips] prove they are identical
* [[Media:FDC9229BT Datasheet.pdf]] - FDC9229BT data separator (that usually assists the uPD765 chip)
* [[Media:DDI Schematic.png]] - DDI-1 Schematic (disc interface for CPC464)
