The floppy disc rotates at a nominal speed of 300rpm, with some tolerance. This tolerance of the FDC has been measured by [[Roudoudou]] to be ±12% (it worked from 220kbits/s to 283kbits/s for a reference of 250kbits/s). [https://64nops.wordpress.com/2021/09/02/a-la-decouverte-du-fdc-episode-4/ Source]
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== Unconnected Pins ==
At the end of a successful read or write command, the program should send a ''Terminal Count'' (TC) signal to the FDC. However, in the CPC the TC pin isn't connected to the I/O bus, making it impossible for the program to confirm a correct operation. For that reason, the FDC will assume that the command has failed, and it'll return both Bit 6 in Status Register 0 and Bit 7 in Status Register 1 set. The program should ignore this error message.
The CPC doesn't support floppy DMA transfers, and the FDC's Interrupt signal isn't used in the CPC.
The FDC controller inside the CPC or in the [[Amstrad External Disk Drive|Amstrad DDI-1]] expansion doesn't have the US1 pin connected. This means it can only select floppy drives 0 and 1, and not drives 2 and 3.
However, the FDC in the [[Vortex Disc Drives|Vortex disc interface]] does have the US1 pin connected, so it can manage up to 4 floppy drives.
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