Next's memory can be paged into the top 16K.
Also in this mode, D3 of port EFF7h can be set to place 16K bank 0 into the bottom 16K, overlaying the ROM.
Writes to ports 7FFDh, DFFDh, 1FFDh and EFF7h, will cause the bottom 16K and the top 16K to remap; if allRAM mode is selected, the entire 64K remaps.
In Pentagon 512K mode, port 7FFDh is extended so that bits D7:D6 augment the bank number in bits D2:D0 to form a 5-bit bank number for the top 16K.
On the ZX Spectrum Next, port 1FFDh continues to function (allRAM mode and ROM selection) and D3 of port EFF7h can be set to map 16K bank 0 on top of ROM in the bottom 16K.
Writes to ports 7FFDh, DFFDh, 1FFDh and EFF7h will cause the bottom 16K and the top 16K to remap; if allRAM mode is selected, the entire 64K remaps.
In Pentagon 1024K mode, port EFF7h D2 = 0 enables Pentagon 1024K mapping and port EFF7h D2 = 1 selects standard ZX Spectrum mapping as described above.
With Pentagon 1024K mode active, port 7FFDh is unlocked and D5 (the lock bit) is repurposed as another bank bit.
The bank number paged into the top 16K is taken as port 7FFDh bits {D5,D7,D6,D2,D1,D0} to reach 1MB in 16K banks.
On the Next, port 1FFDh continues to function (allRAM mode and ROM selection) and D3 of port EFF7h can be set to map 16K bank 0 on top of ROM in the bottom 16K.
Writes to ports 7FFDh, DFFDh, 1FFDh and EFF7h will cause the bottom 16K and the top 16K to remap; if allRAM mode is selected, the entire 64k remaps.
For 100% compatibility with the original banking methods listed above, extra ports like 1FFDh can be disabled using the internal port decodes with NextREGs 130 - 133 (82h - 85h).
The Expansion Bus is found in the back of the ZX Spectrum Next and exposes its CPU to the world. As it too gets addressed by IN and OUT commands, it is listed below:
| Bottom Side | A11 | 28 | 28 | Reserved | Top Side |
|---|---|---|---|---|---|
| A9 | 27 | 27 | A10 | ||
| B̅U̅S̅A̅C̅K̅ | 26 | 26 | A8 | ||
| R̅O̅M̅C̅S̅ | 25 | 25 | R̅F̅S̅H̅ | ||
| A4 | 24 | 24 | M̅1̅ | ||
| A5 | 23 | 23 | NC | ||
| A6 | 22 | 22 | NC | ||
| A7 | 21 | 21 | W̅A̅I̅T̅ | ||
| R̅E̅S̅E̅T̅ | 20 | 20 | NC | ||
| BUSREQ6 | 19 | 19 | W̅R̅ | ||
| NC | 18 | 18 | R̅D̅ | ||
| NC | 17 | 17 | I̅O̅R̅Q̅ | ||
| Reserved | 16 | 16 | M̅R̅E̅Q̅ | ||
| R̅O̅M̅C̅S̅ | 15 | 15 | H̅A̅L̅T̅ | ||
| GND | 14 | 14 | N̅M̅I̅ | ||
| I̅O̅R̅Q̅U̅L̅A̅ | 13 | 13 | I̅N̅T̅ | ||
| A3 | 12 | 12 | D4 | ||
| A2 | 11 | 11 | D3 | ||
| A1 | 10 | 10 | D5 | ||
| A0 | 9 | 9 | D6 | ||
| C̅L̅K̅ | 8 | 8 | D2 | ||
| GND | 7 | 7 | D1 | ||
| GND | 6 | 6 | D0 | ||
| Key | 5 | 5 | Key | ||
| +9V (PSU)7 | 4 | 4 | R̅O̅M̅C̅S̅ | ||
| +5V | 3 | 3 | D7 | ||
| A12 | 2 | 2 | A13 | ||
| A14 | 1 | 1 | A15 |
The ZX Spectrum Next Expansion Bus
6 BUSREQ is incorrectly active High oin Issue 2 but fixed on Issue 4 7: This pin receives the unregulated power from the PSU line. If you plug a higher voltage PSU, that voltage will be present at that pin and may damage your peripherals
ZX Spectrum Next User Manual, 3rd Edition (ISBN 978-1-5272-5496-1), written and illustrated by Phoebus R. Dokos. Copyright © 2020-2024 Phoebus Dokos / SpecNext Ltd. Licensed under CC BY-NC-SA 4.0. This is a transcription and can contain errors; check any doubt against the printed page.