### Next Register Diagrams' Key | Symbol | Meaning | |---|---| | [colour: light green] | Reserved value in either R(ead) or W(rite) condition but used in the inverse – **Not Applicable** | | [colour: dark green] | Reserved value - **Not Applicable** | | [colour: dark green] X | Reserved value **MUST be X** | | [colour: pink] | **Not Applicable / Don't care** | | R | **Read** (if marked). Unmarked means **Not Applicable** | | W | **Write** (if marked). Unmarked means Not Applicable | | H | **Hard** Reset / **Soft** Reset / **Config Mode**. Unmarked means **Soft Reset** if there's a value in column **D** | | D | Contains the default value after a reset (Soft, Hard or Config as marked in column H).**\*** refers to notes below | | ■ | In columns R/W marks the status of the register. In column H means Hard Reset | | ♦ | Means **Config Mode** | | • | Means *any* value (**0** or **1**) | | N | Any letter in a data bit position refers you to the notes below | #### NextREG 00 (00h) – Machine ID

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
Machine ID	■		0	0	0	0	1	0	0	0	EMULATORS
			0	0	0	0	1	0	1	0	ZX Spectrum Next
			1	1	1	1	1	0	1	0	ZX Spectrum Next Anti-Brick
			1	0	0	1	1	0	1	0	Next Core on UnAmiga Reloaded
			1	0	1	0	1	0	1	0	Next Core on UnAmiga
			1	0	1	1	1	0	1	0	Next Core on SiDi
			1	1	0	0	1	0	1	0	Next Core on MiST
			1	1	0	1	1	0	1	0	Next Core on MiSTer
			1	1	1	0	1	0	1	0	Next Core on ZX-DOS/gomaDOS

#### NextREG 01 (01h) – Core Version

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
Minor Version Number	■		[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	•	•	•	•	Minor Version
Major Version Number	■		•	•	•	•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Major Version

See **NextREG 14 (0Eh)** for sub minor version number #### NextREG 02 (02h) – Reset

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
Last System Reset Type	■		[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	0	1	Soft Reset
			[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	1	0	Hard Reset
divMMC NMI source	■		[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	divMMC NMI not generated by NR 02h
			[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	divMMC NMI generated by NR 02h
MF NMI source	■		[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	MF NMI not generated by NR 02h
			[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	MF NMI generated by NR 02h
			[colour: pink]	[colour: dark green]	[colour: dark green]	0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	MF NMI not generated by I/O Trap²,*
			[colour: pink]	[colour: dark green]	[colour: dark green]	1	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	MF NMI generated by I/O Trap²,*
Reserved	■		[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Reserved
ESP/Expansion Bus R̅E̅S̅E̅T̅ flag	■		0	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	R̅E̅S̅E̅T̅ not asserted	■	0
			1	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	R̅E̅S̅E̅T̅ asserted
Generate System Reset		■	[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	0	1	Generate Soft Reset
			[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	1	0	Generate Hard Reset (reboot)
divMMC NMI control		■	[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	•	[colour: pink]	[colour: pink]	Generate/Clear divMMC NMI³
MF NMI control		■	[colour: pink]	[colour: dark green]	[colour: dark green]	[colour: pink]	•	[colour: pink]	[colour: pink]	[colour: pink]	Generate/Clear MF NMI³
			[colour: pink]	[colour: dark green]	[colour: dark green]	•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	If 0 Clear MF I/O Trap²,³
Reserved		■	[colour: pink]	[colour: dark green] 0	[colour: dark green] 0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Reserved (must be 0)
Generate ESP/Exp. Bus Reset¹		■	•	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Generate/Release Reset (Exp. Bus & ESP)

1 A full reset cycle for the ESP and Expansion Bus, requires setting **D7** first to **1** for **at least 100 ms** and then to **0**. The 100 ms assertion is required by the ESP module. If not explicitly released the Expansion Bus and ESP will stay with R̅E̅S̅E̅T̅ asserted until the next system hard reset\ Of **D0** – **D1** Hard Reset has precedence\ ² Experimental\ ³ These signals are ignored if the Multiface, divMMC, DMA or external NMI master is active. Copper cannot clear these bits. Note: An I/O trap could occur at the same time as MF / divMMC cause; always check this bit in NMI ISR if important\ \* See **NextREG 218 (DAh)** #### NextREG 03 (03h) – Machine Type

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
Machine Type	■	■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	0	0	Configuration mode	♦
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	0	1	ZX 48K
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	1	0	ZX 128K / +2
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	1	1	ZX +2A / +2B / +3 / Next
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	1	0	0	Pentagon Clones*
Display Timing user lock control	■		[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	No User Lock on display timing applied
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	User lock on display timing applied
		■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	•	[colour: pink]	[colour: pink]	[colour: pink]	Toggle User Lock on Display Timing	■	0
Display Timing	■	■	[colour: pink]	0	0	0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Internal Use
			[colour: pink]	0	0	1	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	ZX 48K
			[colour: pink]	0	1	0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	ZX 128K / +2
			[colour: pink]	0	1	1	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	ZX +2A / +2B / +3 / Next
			[colour: pink]	1	0	0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Pentagon*
NR 68 (44h) 2nd Byte Indicator	■		•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Palette Entry (NR 68) Second Byte flag		0
Display Timing change enable		■	•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Allow changes to D4:6		0

\* Pentagon timing is **50 Hz** only\ Machine type determines which ROMs are loaded and Display Timing also affects port decoding #### [?]

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
16K RAM bank mapping		■	[colour: dark green]	•	•	•	•	•	•	•	Maps a 16K RAM Bank no. (0-127)*	♦	0
Reserved		■	[colour: dark green] 0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Reserved, must be 0

\* Maps a 16K RAM bank over the **bottom** 16K. Applies only in configuration mode when the boot rom is disabled\ Even multiples of 256K are unreliable if storing data in RAM for the Next Core started #### NextREG 05 (05h) – Peripheral 1 Settings

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
Scandoubler¹	■	■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	Scandoubler Disabled
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	1	Scandoubler Enabled
Vertical Frequency	■	■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	50 Hz mode
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	60 Hz mode*
Joystick 1**	■	■	0	0	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	Sinclair 2 (12345)
			0	0	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	Kempston 2 (Port 37h)
			0	1	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	Kempston 1 (Port 1Fh)
			0	1	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	MD 1 (Port 1Fh)
			1	0	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	Cursor (56780)
			1	0	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	MD 2 (Port 37h)
			1	1	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	Sinclair 1 (67890)
			1	1	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	User Defined Keys Joystick
Joystick 2**	■	■	[colour: pink]	[colour: pink]	0	0	[colour: pink]	[colour: pink]	0	[colour: pink]	Sinclair 2 (12345)
			[colour: pink]	[colour: pink]	0	0	[colour: pink]	[colour: pink]	1	[colour: pink]	Kempston 2 (Port 37h)
			[colour: pink]	[colour: pink]	0	1	[colour: pink]	[colour: pink]	0	[colour: pink]	Kempston 1 (Port 1Fh)
			[colour: pink]	[colour: pink]	0	1	[colour: pink]	[colour: pink]	1	[colour: pink]	MD 1 (Port 1Fh)
			[colour: pink]	[colour: pink]	1	0	[colour: pink]	[colour: pink]	0	[colour: pink]	Cursor (56780)
			[colour: pink]	[colour: pink]	1	0	[colour: pink]	[colour: pink]	1	[colour: pink]	MD 2 (Port 37h)
			[colour: pink]	[colour: pink]	1	1	[colour: pink]	[colour: pink]	0	[colour: pink]	Sinclair 1 (67890)
			[colour: pink]	[colour: pink]	1	1	[colour: pink]	[colour: pink]	1	[colour: pink]	User Defined Keys Joystick

¹ Enabled for VGA / HDMI, Disabled for RGB mode\ \* Pentagon Clones have no 60 Hz mode; when in Pentagon mode, every setting is **50 Hz**.\ \*\* Joystick ports can be placed into I/O mode via **NextREG 11 (Bh)**\ Programming the user defined keys joystick is done through the PS/2 keymap interface on **NextREG 40 (28h)**, **41 (29h)** and **43 (2Bh)**: 1. Write **128** to **NextREG 40 (28h)** 2. Write **0** (Left joystick) or **16** (Right joystick) to **NextREG 41 (29h)** 3. Write **12** bytes to **NextREG 43 (2Bh)** in order. The bytes correspond to the twelve buttons on an MD pad as follows (**Byte 0** to **Byte 11**):\ **R, L, D, U, B, C, A, START, Y, Z, X, MODE** 4. Each byte written identifies a key in the **8x7** membrane; **D5:3** select the row and **D2:0** the column with **111** meaning no action In Kempston and MD modes. excess buttons on an controller not read via ports will generate key input if so programmed #### NextREG 06 (06h) – Peripheral 2 Settings

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
PSG Mode Control	■	■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	0	YM
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	1	AY
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	1	1	Hold all PSGs in Reset
PS/2 Mode Control	■	■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	0	[colour: pink]	[colour: pink]	Keyboard Primary	♦	0
			[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	1	[colour: pink]	[colour: pink]	Mouse Primary
NMI Button Control	■	■	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	•	[colour: pink]	[colour: pink]	[colour: pink]	NMI button enable*	■	0
divMMC NMI Control	■	■	[colour: pink]	[colour: pink]	[colour: pink]	•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	divMMC NMI** button enable	■	0
F3 Hotkey Control	■	■	[colour: pink]	[colour: pink]	•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	50 Hz / 60 Hz hotkey enable		1
Internal Speaker BEEP Control	■	■	[colour: pink]	0	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	All audio copied to speaker	■	0
			[colour: pink]	1	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	Only BEEP sounds diverted to speaker
F5, F6 and F8 Hotkey Control	■	■	•	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	[colour: pink]	CPU Speed and Exp. Bus hotkeys enable		1

\* NMI button refers to the button to the right side of the SD Card reader\ \*\* Refers to the Drive button to the left side of the SD Card reader #### NextREG 07 (07h) – CPU Speed

Group Name	R	W	Data Bits								Description	H	D
			7	6	5	4	3	2	1	0
CPU Speed Control¹	■	■	[colour: dark green]	[colour: dark green]	[colour: light green]	[colour: light green]	[colour: dark green]	[colour: dark green]	0	0	3.5 MHz		*
			[colour: dark green]	[colour: dark green]	[colour: light green]	[colour: light green]	[colour: dark green]	[colour: dark green]	0	1	7 MHz
			[colour: dark green]	[colour: dark green]	[colour: light green]	[colour: light green]	[colour: dark green]	[colour: dark green]	1	0	14 MHz
			[colour: dark green]	[colour: dark green]	[colour: light green]	[colour: light green]	[colour: dark green]	[colour: dark green]	1	1	28 MHz
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
Reserved	■		[colour: dark green] 0	[colour: dark green] 0	[colour: light green]	[colour: light green]	[colour: dark green] 0	[colour: dark green] 0	[colour: pink]	[colour: pink]	Reserved, must be 0
Current Actual² CPU Speed	■		[colour: dark green]	[colour: dark green]	0	0	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	3.5 MHz
			[colour: dark green]	[colour: dark green]	0	1	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	7 MHz
			[colour: dark green]	[colour: dark green]	1	0	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	14 MHz
			[colour: dark green]	[colour: dark green]	1	1	[colour: dark green]	[colour: dark green]	[colour: pink]	[colour: pink]	28 MHz

\* Soft reset defaults this to **00**\ ¹ When read returns the Programmed CPU speed as it may differ from actual speed. See below\ ² Current Actual speed may differ from the set speed due to Expansion Bus use, or another forced change