Here is a list of the port addresses used with their decoding. For the reason mentioned, only the ULA has an even port address and every even-numbered port IN will result in the ULA being read.
| R | W | A15 | A14 | A13 | A12 | A11 | A10 | A9 | A8 | A7 | A6 | A5 | A4 | A3 | A2 | A1 | A0 | Port (Hex) | Description |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ■ | ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | FEh | ULA |
| ■ | ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | FFh | Timex video, Floating bus |
| ■ | 0 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 7FFDh | Memory Paging Control | |
| ■ | 0 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 7FFDh | Memory Paging Control (+3/Next only) | |
| ■ | 1 | 1 | 0 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | DFFDh | Next Memory Bank Select1 | |
| ■ | 0 | 0 | 0 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 1FFDh | +3 Memory Paging Control | |
| ■ | 0 | 0 | 1 | 0 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 2FFDh | +3 FDC Status | |
| ■ | ■ | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 3FFDh | +3 FDC Control |
| ■ | 1 | 1 | 1 | 0 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | EFF7h | Pentagon 1024K Memory Paging Cntl. | |
| ■ | 0 | 0 | 0 | 0 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | +3 Floating bus | ||
| ■ | ■ | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 243Bh | NextREG Select |
| ■ | ■ | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 253Bh | NextREG Data |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 103Bh | I²C SCL |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 113Bh | I²C SDA |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 123Bh | Layer 2 |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 133Bh | UART Tx |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 143Bh | UART Rx |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 153Bh | UART Select |
| ■ | ■ | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 163Bh | UART Frame |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 183Bh | CTC Channel 02 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 193Bh | CTC Channel 12 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 1A3Bh | CTC Channel 22 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 1B3Bh | CTC Channel 32 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | colour: light orange 1C3Bh | colour: light orange CTC Channel 42 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | colour: light red 1D3Bh | colour: light red CTC Channel 52 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | colour: light orange 1E3Bh | colour: light orange CTC Channel 62 |
| ■ | ■ | 0 | 0 | 0 | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | colour: light red 1F3Bh | colour: light red CTC Channel 72 |
| ■ | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | BF3Bh | ULAplus Register | |
| ■ | ■ | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | FF3Bh | ULAplus Data |
| ■ | ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 0Bh | z80DMA3 |
| ■ | ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 6Bh | zxnDMA3 |
| ■ | ■ | 1 | 1 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 0 | 1 | FFFDh | AY Register |
| ■ | ■ | 1 | 0 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 0 | 1 | BFFDh | AY Data (readable on +3/Next only) |
| ■ | 1 | 0 | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 0 | 1 | BFF5h | AY Inf (inside BFFDh decoding) | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1Fh | DAC A | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | F1h | DAC A4 | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 3Fh | DAC A | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 0Fh | DAC B | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | F3h | DAC B | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | DFh | DAC A,D | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | FBh | DAC A,D | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | B3h | DAC B,C | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 4Fh | DAC C | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | F9h | DAC C4 | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 5Fh | DAC D | |
| ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | E7h | SPI CS (SD card, Flash, RPi0) | |
| ■ | ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | EBh | SPI DATA |
| ■ | ■ | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | colour: pale pink | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | E3h | divMMC control |
1 Precedence over AY 2: Temporarily reduced to first four CTC channels only 3: Selecting either DMA port, also selects the mode in which the DMA operates 4: Precedence over xxFD
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.