On Fri, 7 Dec 2001, Eric Boon wrote: > > It's accessed using MREQ# rather than IORQ#. > > Are you saying you don't have > > to select slot 3 in order to change it? > > Yes
Curious. > > In which case, does it affect other expanded slots also? > > Yes, but since you have the *primary* slot (I/O port #A8) > set toa certain slot, switching expanded slots in other > primary slots doesn't make a difference. I think I understand what you mean. > > ie. is it possible to have more than one > > secondary slot register, on a per slot basis, > > No. That's curious. Surely you can decode #FFFF on a cartridge and do what you like with the bits? > > or does writing to the same register affect all slots? > > Yes :-) I guess there are secondary slot select outputs on the cartridge slot. > > Presumably when the RAM at #C000 - #FFFF is enabled, writing to this > > register will also "write through" to the RAM at location #FFFF, so that > > reading from this location will return the last value written to the > > register. (?) > > Reading #FFFF will return the *inverse* of what you've written into > it (don't ask ;-)). I guess it will depend on the hardware whether the byte > written to #FFFF will ever land in RAM... > (AFAIK, all of this should be in the MSX Red Book, by the way, > which is available from ftp://ftp.funet.fi/pub/txt/tech/tredbook.arj) Well there seems to be a bit of variation even on msx-list about what the hardware does, but this bit at least is consistent and is enough for me to correct my routine. As long as the register accesses are properly nested the situations described above won't affect the routine. Thanks everyone for all your help. When I next get a chance to work on the CX5MII/128 I'll hopefully have some useful results for you. In the meantime, I will post in a follow-up email the results of my MSX-Audio test register experiments I did last weekend. Richard -- For info, see http://www.stack.nl/~wynke/MSX/listinfo.html
