I recently bought a Philips VG 8235 with a PC diskdrive. It seems that I am able to use HD disks on the MSX computer (holes not covered). Is that supposed to work?
The FDCs of the MSX are not clocked in the way, that would make reading HD discs possible.
Maybe you can modify your disc rom + writing fast enough routines, so that the Z80 can read the double speeded data stream of a HD disc, but your FDC would still fail.
The HD disks could only be read after I formatted them on the MSX. However, I thought that I couldn´t even format HD disks on the MSX-computer without covering the holes.