From SpecNext official Wiki
|Short desc.||Divmmc control|
0xE3 Divmmc control
- bit 7 = conmem = 1 to map in divmmc, 0K-8K will contain the esxdos rom, 8K-16K will contain the selected divmmc bank
- bit 6 = mapram = 1 to replace the esxdos rom with divmmc bank 3
- bits 3:0 = bank = selected divmmc ram bank for 8K-16K region
- conmen can be used to manually control divmmc mapping.
- divmmc automatically maps itself in when instruction fetches hit specific addresses in the rom. When this happens, the esxdos rom (or divmmc bank 3 if mapram is set) appears in 0K-8K and the selected divmmc bank appears as ram in 8K-16K.
- bit 6 can only be set, once set only a power cycle can reset it on the original divmmc.
nextreg 0x09 bit 3 can be set to reset this bit.
The divmmc has been enhanced in the zx next to add more entry points and make them programmable. See nextreg 0xB8 - 0xBB.