Changes

Before accessing a disk you should first "Recalibrate" the drive, that moves the head backwards until it reaches Track 0. (The Track 0 signal from the drive is sensed by the FDC and it initializes it's internal track counter for that drive to 0).  On a 80 track drive you may need to repeat that twice because some models of the FDC stop after 77 steps and if your recalibrating from track 80 it will not recalibrate fully. Now if you want to format, read or write a sector on a specific track you must first Seek that track (command 0Fh). That'll move the read/write head to the physical track number. If you don't do that, then the FDC will attempt to read/write data to/from the current physical track, independendly independenly of the specified logical Track-ID.

Despite of the confusing name, a sector with a "Deleted Data Address Mark" (DAM) is not deleted. The DAM-flag is just another ID-bit, and (if that ID-bit is specified correctly in the command) it can be read/written like normal data sectors.

At the end of a successful read/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 errormessageerror message.

Usually single sided 40 Track 3" disk drives are used in CPCs, whereas 40 tracks is the official specification, practically 42 tracks could be used(the limit is specific to the FDD, some support more tracks. 42 is a good maximum). The FDC controller can be used to control 80 tracks, and/or double sided drives also, even though AMSDOS isn't supporting such formats. AMSDOS is supporting a maximum of two disk drives only.