Board feature control

	Number	Readable	Writable	Description
Machine ID Register	$00	true	false	Identifies TBBlue board type. Should always be 10 (binary 0000 1010) on Next.
Core Version Register	$01	true	false	Identifies core (FPGA image) version.
Next Reset Register	$02	true	true	Identifies type of last reset. Can be written to force reset.
Machine Type Register	$03	true	true	Identifies timing and machine type.
Config Mapping Register	$04	false	true	In config mode, allows RAM to be mapped to ROM area.
Peripheral 1 Register	$05	true	true	Sets joystick mode, video frequency and Scandoubler.
Peripheral 2 Register	$06	true	true	Enables CPU Speed key, DivMMC, Multiface, Mouse and AY audio.
CPU Speed Register	$07	true	true	Sets CPU Speed, reads actual speed.
Peripheral 3 Register	$08	true	true	ABC/ACB Stereo, Internal Speaker, SpecDrum, Timex Video Modes, Turbo Sound Next, RAM contention and [un]lock 128k paging.
Peripheral 4 Register	$09	true	true	Sets scanlines, AY mono output, Sprite-id lockstep, reset DivMMC mapram and disable HDMI audio.
Peripheral 5 Register	$0A	true	true	Multiface type, Divmmc automap, Mouse buttons and DPI config
Joystick I/O Mode	$0B	true	true	Joystick port I/O control
Core Version Register (sub minor)	$0E	true	false	Identifies core (FPGA image) version (sub minor number).
Board ID	$0F	true	false	Spectrum next issue ID
Anti-brick Register	$10	true	true	Used within the Anti-brick system.
Video Timing Register	$11	true	true	Sets video output timing variant.
Layer 2 RAM Page Register	$12	true	true	Sets the bank number where Layer 2 video memory begins.
Layer 2 RAM Shadow Page Register	$13	true	true	Sets the bank number where the Layer 2 shadow screen begins.
Global Transparency Register	$14	true	true	Sets the "transparent" colour for Layer 2, ULA and LoRes pixel data.
Sprite and Layers System Register	$15	true	true	Enables/disables Sprites and Lores Layer, and chooses priority of sprites and Layer 2.
Layer 2 X Offset Register	$16	true	true	Sets the pixel offset used for drawing Layer 2 graphics on the screen.
Layer 2 Y Offset Register	$17	true	true	Sets the Y offset used when drawing Layer 2 graphics on the screen.
Clip Window Layer 2 Register	$18	true	true	Sets and reads clip-window for Layer 2.
Clip Window Sprites Register	$19	true	true	Sets and reads clip-window for Sprites
Clip Window ULA/LoRes Register	$1A	true	true	Sets and reads clip-window for ULA/LoRes layer.
Clip Window Tilemap Register	$1B	true	true	Sets and reads clip-window for Tilemap.
Clip Window Control Register	$1C	true	true	Controls (resets) the clip-window registers indices.
Active Video Line MSB Register	$1E	true	false	Holds the MSB (only, as bit 0) of the raster line currently being drawn.
Active Video Line LSB Register	$1F	true	false	Holds the eight LSBs of the raster line currently being drawn.
Generate Maskable Interrupt	$20	true	true	Trigger interrupt
Video Line Interrupt Control Register	$22	true	true	Controls the timing of raster interrupts and the ULA frame interrupt.
Video Line Interrupt Value Register	$23	true	true	Holds the eight LSBs of the line on which a raster interrupt should occur.
Reserved	$24	false	false	n/a
ULA X Offset Register	$26	true	true	Pixel X offset (0..255) to use when drawing ULA Layer.
ULA Y Offset Register	$27	true	true	Pixel Y offset (0..191) to use when drawing ULA Layer.
Keymap High Address Register	$28	true	true	PS/2 Keymap address MSB, read (pending) first byte of palette colour
Keymap Low Address Register	$29	false	true	PS/2 Keymap address LSB.
Keymap High Data Register	$2A	false	true	High data to PS/2 Keymap (MSB of data in bit 0)
Keymap Low Data Register	$2B	false	true	Low eight LSBs of PS/2 Keymap data.
DAC B (left) mirror Register	$2C	true	true	DAC B mirror, read current I2S left MSB
DAC A+D (mono) mirror Register	$2D	true	true	SpecDrum port 0xDF / DAC A+D mirror, read current I2S LSB
DAC C (right) mirror Register	$2E	true	true	DAC C mirror, read current I2S right MSB
Tilemap Offset X MSB Register	$2F	true	true	Sets the pixel offset (two high bits) used for drawing Tilemap graphics on the screen.
Tilemap Offset X LSB Register	$30	true	true	Sets the pixel offset (eight low bits) used for drawing Tilemap graphics on the screen.
Tilemap Offset Y Register	$31	true	true	Sets the pixel offset used for drawing Tilemap graphics on the screen.
LoRes X Offset Register	$32	true	true	Pixel X offset (0..255) to use when drawing LoRes Layer.
LoRes Y Offset Register	$33	true	true	Pixel Y offset (0..191) to use when drawing LoRes Layer.
Sprite port-mirror Index Register	$34	true	true	Selects sprite index 0..127 to be affected by writes to other Sprite ports (and mirrors).
Sprite port-mirror Attribute 0 Register	$35	false	true	Nextreg port-mirror to write directly into "byte 1" of Sprite Attribute Upload ($xx57 / 87).
Sprite port-mirror Attribute 1 Register	$36	false	true	Nextreg port-mirror to write directly into "byte 2" of Sprite Attribute Upload ($xx57 / 87).
... further results