Next Memory Bank Select
From SpecNext official Wiki
| Number | $DFFD |
|---|---|
| Decimal | |
| Short desc. | Provides additional bank select bits for extended memory. |
| Bit Mask | %1101 1111 1111 1101 |
| Readable | No |
| Writable | Yes |
| Subsystem | Memory map |
- bit 7 = 1 to set pentagon 512K mode (hard reset = 0) †
- bits 3:0 = most significant bits of the 16K RAM bank selected in Memory Paging Control ($7FFD / 32765) (soft reset = 0)
Port 0xDFFD bits 3:0 are combined as the highest bits with the bank selected in port 0x7FFD to form a 7-bit bank number.
Bit 7 can only be modified when pentagon timing is not active.
† Pentagon 512K mode is applied only when the machine is set to pentagon timing (Machine Type Register ($03)). In this mode the selected 16K bank comes from port 0x7ffd {bits 7:6, bits 2:0}