MSX Assembly Page

Thanks, interesting… Knew about the JIS1 bit but not the others…

Thanks! Added.

Am I right to think that one is MSX2 and up only? (And on MSX1 it’s FCC1H?)

That is a bold statement! What is the source of that statement ?
The only problem with expanding slot 0 on MSX1 is that the first version of the MSX1 BIOS does not handle this well. The later version of the MSX1 BIOS (for example in the Philips VG8020/20 and Yamaha CX5MII128) does fix this.
See http://msxsyssrc.cvs.sourceforge.net/viewvc/msxsyssrc/base100/bios.mac,look for SLOTFIX.

Ok, I can only find reference to FFF7H in the MSX2 BIOS (subrom), so I’ll add a note that it’s MSX2 and up only.

*speculation follows*

I recall now that I previously theorised that FFF7H was added as an alternative to FCC1H in MSX2 to support MSX1 to MSX2 upgrade cartridges which replace the BIOS. Needed because FCC1H only supports slot IDs 0 and 0-0 due its dual function as EXPTBL entry for slot 0.

Although if this is true, then in practice it’s failed that purpose and is not a usable solution, since probably a lot of MSX2 software uses FCC1H, including official documentation. I think it was doomed to fail, even if the docs had been clear about this, it’d still have been difficult to guarantee all MSX2 software would use the new address with so much existing MSX1 documentation pointing to FCC1H.

My guess is that this mythical MSX2 upgrade kit was mostly a sales pitch to hardware vendors and end users that they made a half-hearted attempt to support, but never put real effort into. Perhaps due to lack of vendor interest to develop or support such kits when they could also sell new computers, or because such a Frankenstein-upgrade simply wasn’t really possible in the then-current architecture while retaining an acceptable level of compatibility.

Too bad. May be that was the plan.
But not workable because official documentation (also pre MSX2) states that the slotid of the mainrom was either slot 0 or if slot 0 was expanded, 0-0. In example code and in system software (disk,rs232) the slotid of the mainrom was always loaded from (EXPTBL+0). This because (EXPTBL+0) contains 0 if slot 0 was not expanded and 080H if slot 0 was expanded. And this matches exactly with the slotid of the mainrom in both cases (non expanded slot 0 and expanded slot 0).
Now comes the problem with the upgrade kits.... The normal system software must continue to work with the kit. But the kit needs to make sure the new mainrom is being used (instead of the orginal mainrom of the upgraded MSX). The only way to fix this, is by putting the slotid of the new mainrom at (EXPTBL+0). This is exactly how the NEOS MA-20 upgrade kit works. In fact the NEOS MA-20 even sets expanded slot bit, even when the NEOS MA-20 is in a normal primairy slot. This makes all the normal system software working with the new NEOS MA-20 mainrom, but the down site is that the expanded slot flag of primary slot 0 (which was on (EXPTBL+0) according to the MSX1 standard) is unreliable. MSX2 documentation is a bit unclear about this point.
About (0FFF7H), is always set to the content of (EXPTBL+0) on MSX2 and up. On MSX1 (0FFF7H) is not initialized, so you can not be sure about the value (could be anything, may be 0, may be 0FFH, you really can not tell). (0FFF7H) is not used in any system software, any coding example I know of and official documentation does not even mention it.

@sd_snatcher thanks for welcoming me back. I never did stop reading msx.org (anonymous) but login only to make comments when needed :-)