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	Number	Readable	Writable	Description
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).
Sprite port-mirror Attribute 2 Register	$37	false	true	Nextreg port-mirror to write directly into "byte 3" of Sprite Attribute Upload ($xx57 / 87).
Sprite port-mirror Attribute 3 Register	$38	false	true	Nextreg port-mirror to write directly into "byte 4" of Sprite Attribute Upload ($xx57 / 87).
Sprite port-mirror Attribute 4 Register	$39	false	true	Nextreg port-mirror to write directly into "byte 5" of Sprite Attribute Upload ($xx57 / 87).
Palette Index Register	$40	true	true	Chooses an palette element (index) to manipulate with