Andrew Collier wrote: > HMPR (251dec) bit 7 MCNTRL > If this bit is set when the CPU addresses high memory, then the external > signal XMEM goes low and the Coupe looks on its expansion connector for > memory sections C and D (addresses 32768 to 65536) > > This isn't enough information. I'm pretty certain there are another two > ports, one each to specify a page in sections C and D. But I've no idea > what port addresses they're at.
Port 0x80 is the external page for section C, and port 0x81 is for section D. As you said above bit 7 of HMPR has to be set for these to be visible, and the page in section D appears to cover ROM1 when paged in too. The other important things is that each extra MB added is present from the top of memory down. If you have the maximum 4MB then all external pages from 0 to 255 are available, but if you have 3MB then only 64-255 are valid (128-255 for 2MB and 192-255 for 1MB). > Over to... Si? Well, over to the SimCoupe source - I don't have any external memory either! Si
