Turning Philips VG-8230 into a normal MSX2

By Alexey

Guardian (3093)

Alexey's picture

10-05-2021, 17:02

Recently I had to modify a few Philips VG823x computers - to change disk ROMs to the ones, supporting double-sided floppy drives or Gotek emulators (by default 8230 and 8235 had single-side drives installed). For the 8235 models everything went fine, but with 8230 there appeared to be a problem. Disk games without MSX-DOS were loading fine, but when trying to load MSX-DOS, everything froze. After consulting RepairBas I learned that the motherboard on 8230 was quite buggy and DOS could not be loaded without the special modification. Philips could not fix the problem easily, so they decided to make a new revision of the board and started to sell it as 8235/00. Looks like the RAM management didn't work properly on 8230.

RepairBas offered the fix that would eliminate the bug on the 8230's motherboard. The fix was installed and confirmed to be working. After the fix MSX-DOS was running correctly from double-sided floppy drives or Gotek emulators. Below you can find the description of the modification, so you can turn your 8230 into the proper MSX2 computer with 720kb disk drive.

http://rbsc.su/files/VG8230_DS_FDD.pdf

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By zeilemaker54

Champion (298)

zeilemaker54's picture

11-05-2021, 20:32

Alexey wrote:

RepairBas offered the fix that would eliminate the bug on the 8230's motherboard.

In my opion, this is not a real bug. The VG8230 does not feature the mapping of the FDC (mirroring) in page 2 as the VG8235 and later Philips MSX2 computers. The lack of the FDC mirroring also means you can not use a FDC ROM of a VG8235 or later (which is using this feature). The 'fix' of RepairBas just adds the FDC mirroring feature.

By sdsnatcher73

Paragon (1862)

sdsnatcher73's picture

11-05-2021, 21:44

Thanks for the explanation! So actually if a 720kB diskROM was modified so it would not rely on mirroring of the FDC registers that would also do the trick? Or maybe a diskROM of some other machine that does not have mirrored FDC registers?

By zeilemaker54

Champion (298)

zeilemaker54's picture

12-05-2021, 17:16

sdsnatcher73 wrote:

So actually if a 720kB diskROM was modified so it would not rely on mirroring of the FDC registers that would also do the trick?

Yes, that is correct.

sdsnatcher73 wrote:

Or maybe a diskROM of some other machine that does not have mirrored FDC registers?

Yes, also correct.
But most FDC designs did implement the mirroring (and the disk driver is using the mirroring), because that has the advantage of a direct sector transfer to page 0 or 1 in MSXDOS (which is faster) instead of using the sector buffer as a temporary store.