Maarten ter Huurne schreef: > At 04:55 PM 5/20/98 +0200, you wrote: > > >The standard does not say that mapper register may be read. according to the msx technical data book msx2 memory mapper specification the can be read back , and the do not say it's not allowed. turbo r must be compatible with msx2 ..... > > They would have saved a lot of trouble if they stated it more explicit... > > >As far as I know the only problem child with the mapper-page-read-back > >method is the turbo-R... > > Also some MSX2+ models. > > >hmmmm.... if this readback would be the standard, 4 bytes of data RAM > would >be saved, even more > >would be save because the opcodes to read them are shorter... > > All mappers use ports FC-FF. More than one mapper can be present in a > system. When writing, no problem, all mappers accept the same value. When > reading, there is a problem when two mappers want to return different > values (for example because they are not equally large). > this is a real problem , according to the msx standard it's not allowed to have more then 1 mapper (you can not have more then one i/o device on the same port) it's normaly not a problem to have 2 mappers becourse the will read back the same value. when on mapper is bigger then the other one the unused bits must be left free so that the biggest mapper can use those bits. some msx will fail to do this , this can even damage your hardware when using an external mapper. (one mapper will read 0 and the other 1 on the same time) erik -- >
begin: vcard fn: erik de Boer n: de Boer;erik org: chaos email;internet: [EMAIL PROTECTED] x-mozilla-cpt: ;0 x-mozilla-html: FALSE version: 2.1 end: vcard
begin: vcard fn: erik de Boer n: de Boer;erik org: chaos email;internet: [EMAIL PROTECTED] x-mozilla-cpt: ;0 x-mozilla-html: FALSE version: 2.1 end: vcard
