On Mon, 2 May 2005, FRS wrote: > > I switched the CS (CE) signals! > > 27C256 pin 20 to 74LS139 pin 11 > > 61256 pin 20 to 74LS139 pin 12 > > There's no mappertype, since it's 32KB plain ROM. The extra-mirroring is > being caused by some wrong wiring, probably. By doing the > quick-and-dirty method you should get the following layout: > > 0000h-2fffh = EPROM's respective address > 3000h-3fffh = SRAM's respective address > 4000h-6fffh = EPROM's respective address > 7000h-7fffh = SRAM, mirror of 3000h-3fffh > > 8000h-afffh = EPROM, mirror of 0000h-2fffh (*1) > b000h-bfffh = SRAM, mirror of 3000h-3fffh (*1) > > *1: This only happens on the quick-and-dirty method, and is ignored by > the BIOS.
I have a quick question - the diagram online still shows 27C256 pin 20 connected to 74LS139 pin 12 and 6164 pin 20 connected to 74LS139 pin 11. Should these two signals be swapped? JP Grobler mentions he swapped them; I think in order to get the memory map above they do need to be swapped. I'll probably build this as a seperate ROM cartridge; my Toshiba unit is already stuffed full of the 41256 sample DRAM mod and it would be difficult to squeeze an extra SRAM chip into it. With the Toshiba ROM removed it's effectly an I/O device only, so an MSX-AUDIO ROM BIOS cartridge could be plugged into a different slot. Richard _______________________________________________ MSX mailing list ([email protected]) Info page: http://lists.stack.nl/mailman/listinfo/msx
