Page 240 | ZX Spectrum Next User Manual, 3rd Edition

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Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
AFTER SOFT RESET (Copied into bits D4 through D7)
ROM 0 (128K) Lock Enable	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	ROM 0 Lock Enable*	■	0
ROM 1 (48K) Lock Enablen	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	ROM 1 Lock Enable*	■	0
ALT ROM Availability Switch	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	ALT ROM visible ONLY during writes	■	0
ALT ROM Enable	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	ALT ROM Enable	■	0
IMMEDIATE
ROM 0 (128K) Lock Enable	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	ROM 0 Lock Enable*	■	0
ROM 1 (48K) Lock Enable	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	ROM 1 Lock Enable*	■	0
ALT ROM Availability Switch	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	ALT ROM visible ONLY during writes	■	0
ALT ROM Enable	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	ALT ROM Enable	■	0

* The locking mechanism applies also if the alternative ROM is not enabled. For the +3/+3e and Next personalities if the two lock bits are not 0, then the corresponding ROM page is locked in place. Other personalities (models) use the bits to preferentially lock the corresponding 48K or 128K ROM in place

NextREG 142 (8Eh) – ZX Spectrum 128K Memory Mapping

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
RAM bank 0-15	■	■	colour: pink	•	•	•	colour: pink	colour: pink	colour: pink	colour: pink	Port 7FFDh D2:D0
RAM bank 0-15	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Port DFFDh D0
RAM bank in ports 7FFDh, DFFDh paging mode	■		colour: pink	colour: pink	colour: pink	colour: pink	1	colour: pink	colour: pink	colour: pink	Returns 1		1
		■	colour: pink	colour: pink	colour: pink	colour: pink	0	colour: pink	colour: pink	colour: pink	No change in RAM bank / MMU 6 / MMU 7
		■	colour: pink	colour: pink	colour: pink	colour: pink	1	colour: pink	colour: pink	colour: pink	Change RAM bank
Normal Paging Mode		■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	0	colour: pink	colour: pink	Port 1FFDh D0
			colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Port 7FFDh D4
			colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Port 1FFDh D2
allRAM Paging Mode		■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	1	colour: pink	colour: pink	Port 1FFDh D0
			colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Port 1FFDh D1
			colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Port 1FFDh D2

Writes can affect all ports 7FFDh, DFFDh, 1FFDh
Writes always change the ROM / allRAM mapping
Writes immediately change the current MMU mapping as if by Port Write

NextREG 143 (8Fh) – Memory Mapping Mode Control

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Memory Mapping Mode*	■	■	colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	0	0	Standard ZX 128K / +3¹	■	0
			colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	0	1	Reserved
			colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	1	0	Pentagon 512K²
			colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	colour: dark green	1	1	Pentagon 1024K³
Reserved	■	■	colour: dark green 0	colour: dark green 0	colour: dark green 0	colour: dark green 0	colour: dark green 0	colour: dark green 0	colour: pink	colour: pink	Reserved, must be 0

1 Principally ports 7FFDh, DFFDh and 1FFDh
2 Principally port 7FFDh
3 768 Kb on unexpanded Next machines. Principally ports 7FFDh and EFF7h
* The mapping modes affect how ports 7FFDh, DFFDh, 1FFDh and EFF7h carry out memory paging

NextREG 144 (90h) – PI GPIO Pin Output Enable 1/4

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 0	■		colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Pin 0 cannot be enabled		0
Pin 1	■		colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Pin 1 cannot be enabled		0
Pin 2	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Enable		0
Pin 3	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Enable		0
Pin 4	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 5	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 6	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 7	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0

NextREG 145 (91h) – PI GPIO Pin Output Enable 2/4

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 8	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Enable		0
Pin 9	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Enable		0
Pin 10	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Enable		0
Pin 11	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Enable		0
Pin 12	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 13	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 14	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 15	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0

NextREG 146 (92h) – PI GPIO Pin Output Enable 3/4

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 16	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Enable		0
Pin 17	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Enable		0
Pin 18	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Enable		0
Pin 19	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Enable		0
Pin 20	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 21	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 22	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0
Pin 23	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Enable		0

NextREG 147 (93h) – PI GPIO Pin Output Enable 4/4 (MSB)

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 24	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Enable		0
Pin 25	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Enable		0
Pin 26	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Enable		0
Pin 27	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Enable		0

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Group Name	R	W	7	6	5	4	3	2	1	0	Description	D
Pin 0	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Data	1
Pin 1	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Data	1
Pin 2	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Data	1
Pin 3	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Data	1
Pin 4	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	Data	1
Pin 5	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data	1
Pin 6	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data	1
Pin 7	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data	1

NextREG 153 (99h) – PI GPIO Pin State 2/4

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 8	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Data		1
Pin 9	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Data		0
Pin 10	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Data		0
Pin 11	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Data		0
Pin 12	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	Data		0
Pin 13	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data		0
Pin 14	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data		0
Pin 15	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data		0

NextREG 154 (9Ah) – PI GPIO Pin State 3/4

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 16	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Data		0
Pin 17	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Data		0
Pin 18	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Data		0
Pin 19	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Data		0
Pin 20	■	■	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	Data		0
Pin 21	■	■	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data		0
Pin 22	■	■	colour: pink	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data		0
Pin 23	■	■	•	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	Data		0

NextREG 155 (9Bh) – PI GPIO Pin State 4/4 (MSB)

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Pin 24	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Data		0
Pin 25	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	Data		0
Pin 26	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Data		0
Pin 27	■	■	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	colour: pink	Data		0

Writes to the above registers only propagate to the PI GPIO when the corresponding pin has its output enabled by NextREG 144 (90h) to 147 (93h)

NextREG 160 (A0h) – PI Peripheral Enable

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Enable SPI	■	■	colour: dark green	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green	colour: dark green	•	Enable SPI on GPIO 7,8,9,10,11 *		0
Reserved	■	■	colour: dark green	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green 0	colour: dark green 0	colour: pink	Reserved, must be 0
Enable I2C	■	■	colour: dark green	colour: dark green	colour: pink	colour: pink	•	colour: dark green	colour: dark green	colour: pink	Enable I2C on GPIO 2,3 *		0
PI Communication Type	■	■	colour: dark green	colour: dark green	colour: pink	0	colour: pink	colour: dark green	colour: dark green	colour: pink	Connect Rx to GPIO 15, Tx to GPIO 14¹,*		0
PI Communication Type	■	■	colour: dark green	colour: dark green	colour: pink	1	colour: pink	colour: dark green	colour: dark green	colour: pink	Connect Rx to GPIO 14, Tx to GPIO 15 ²,*		0
Enable UART³	■	■	colour: dark green	colour: dark green	•	colour: pink	colour: pink	colour: dark green	colour: dark green	colour: pink	Enable UART on GPIO 14,15 *		0
Reserved	■	■	colour: dark green 0	colour: dark green 0	colour: pink	colour: pink	colour: pink	colour: dark green	colour: dark green	colour: pink	Reserved, must be 0

* Overrides GPIO Enables
1 For communication with Pi HATS
2 For communication with Pi
3 GPIO 16, 17 will act as RTR_n and CTS_n if the UART is in Hardware Flow Control Mode

NextREG 162 (A2h) – PI I²S Audio Control

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
Redirect to EAR	■	■	colour: pink	colour: pink	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green	•	Direct I²S audio to EAR on port 0xFE		0
Reserved	■	■	colour: pink	colour: pink	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green 1	colour: pink	Reserved, must be 1		1
Mute R control	■	■	colour: pink	colour: pink	colour: dark green	colour: pink	colour: pink	•	colour: dark green	colour: pink	Mute right side		0
Mute L control	■	■	colour: pink	colour: pink	colour: dark green	colour: pink	•	colour: pink	colour: dark green	colour: pink	Mute left side		0
Audio flow direction	■	■	colour: pink	colour: pink	colour: dark green	0	colour: pink	colour: pink	colour: dark green	colour: pink	PCM_DOUT to Pi, PCM_DIN from Pi (Hats)		0
Audio flow direction	■	■	colour: pink	colour: pink	colour: dark green	1	colour: pink	colour: pink	colour: dark green	colour: pink	PCM_DOUT from Pi, PCM_DIN to Pi (pi)		0
Reserved	■		colour: pink	colour: pink	colour: dark green 0	colour: pink	colour: pink	colour: pink	colour: dark green	colour: pink	Reserved, must be 0
I²S state	■	■	0	0	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green	colour: pink	I²S Disabled		*
			0	1	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green	colour: pink	I²S is mono, source R
			1	0	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green	colour: pink	I²S is mono, source L
			1	1	colour: dark green	colour: pink	colour: pink	colour: pink	colour: dark green	colour: pink	I²S is stereo

* Soft reset sets a default of 00

NextREG 168 (A8h) – ESP WiFi GPIO Output Control

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
GPIO 0 Output Control	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	GPIO 0 Output Enable		0
GPIO 2 Output Control	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	0	colour: pink	colour: pink	GPIO 2 Output Enable¹		0

1 Fixed at 0; GPIO 2 is Read-Only

NextREG 169 (A9h) – ESP WiFi GPIO Control

Group Name	R	W	Data Bits								Description	H	D
Group Name	R	W	7	6	5	4	3	2	1	0	Description	H	D
GPIO 0	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	Read / Write GPIO 0		1
GPIO 2	■	■	colour: pink	colour: pink	colour: pink	colour: pink	colour: pink	•	colour: pink	colour: pink	Read / Write GPIO 2		1

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.