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#FBF6 Vortex Disc Drives Standard Addresses (same as used by AMSDOS): FB7Eh 765 FDC (internal) Status Register (R) FB7Fh 765 FDC (internal) Data Register (R/W) Special Addresses (secondary FDC): FBF6h 765 FDC (Vortex,ext) Status Register (Read)#FBF7 Vortex Disc Drives FBF7h 765 FDC (Vortex,ext) Data Register (R/W) (The Special addresses are mentioned in the manual for the Vortex -X drives) (but apparently they are referring to other/older Vortex drives, not the -X drives) The Special addresses are used only on CPC 664/6128 and only if the Vortex drive includes an FDC chip. * Note1: The -Z and -X drives do not include FDC chips.* Note2: The -S and -D drives do reportedly work only on CPC 464 (?). So, not sure if/when the Special addresses are used at all?  RS232 Ports (for -X drives with RS232) FADC/FADD=Serial Data/Control FBDC/FBDD/FBDF=Counter 0/1/Mode. So it's probably compatible with Amstrad/Pace (and probably also including, but not using, Channel B Ports FADE/FADF and FBDE).