#### [?]
Group NameRW76543210DescriptionHD
Coordinate (Xbeg,Xend,Ybeg,Yend)■■••••••••8-bit value Xbeg,Xend,Ybeg,Yend coordinate¹*
1 1st Write **X**beg position – \*Resets to **0**\ 2nd Write **X**end position – \*Resets to **255**\ 3rd Write **Y**beg position – \*Resets to **0**\ 4rh Write **Y**end position – \*Resets to **191**\ Reads do not advance the clip position – Use **NR 28 (1Ch) D2:D3** to read the position. If need be, write to **NR 28 (1Ch):D1** to reset the clip index. When the clip window is enabled for sprites in **over border** mode, the **X** coordinates are internally doubled and the clip window origin is moved to the sprite origin inside the border #### NextREG 26 (1Ah) – Layer 0 (ULA/LoRes) Clip Window Definition
Group NameRWData BitsDescriptionHD
76543210
Coordinate (Xbeg,Xend,Ybeg,Yend)■■••••••••8-bit value Xbeg,Xend,Ybeg,Yend coordinate¹*
1 1st Write **X**beg position – \*Resets to **0**\ 2nd Write **X**end position – \*Resets to **255**\ 3rd Write **Y**beg position – \*Resets to **0**\ 4rh Write **Y**end position – \*Resets to **191**\ Reads do not advance the clip position – Use **NR 28 (1Ch) D4:D5** to read the position. If need be, write to **NR 28 (1Ch):D2** to reset the clip index\ **NOTE:** LoRes may get a separate clip window in the future #### NextREG 27 (1Bh) – Layer 3 (Tilemap) Clip Window Definition
Group NameRWData BitsDescriptionHD
76543210
Coordinate (Xbeg,Xend,Ybeg,Yend)■■••••••••8-bit value Xbeg,Xend,Ybeg,Yend coordinate¹*
¹ 1st Write **X**beg position – \*Resets to **0**\ 2nd Write **X**end position – \*Resets to **159**\ 3rd Write **Y**beg position – \*Resets to **0**\ 4rh Write **Y**end position – \*Resets to **255**\ Reads do not advance the clip position – **NR 28 (1Ch) D6:D7** reads the position. If need be, write to **NR 28 (1Ch):D3** to reset the clip index and then do consecutive writes and reads to get to the value you're searching for. The **X** coordinates are internally doubled #### NextREG 28 (1Ch) – Clip Windows Control
Group NameRWData BitsDescriptionHD
76543210
Layer 2 Clip Index■[colour: pink][colour: pink][colour: pink][colour: pink][colour: pink][colour: pink]••Layer 2 Clip Index (0 – 3)
Sprites Layer Clip Index■[colour: pink][colour: pink][colour: pink][colour: pink]••[colour: pink][colour: pink]Sprites Clip Index (0 – 3)
Layer 0 / 1 Clip Index■[colour: pink][colour: pink]••[colour: pink][colour: pink][colour: pink][colour: pink]ULA / Timex Clip Index (0 – 3)
Layer 3 Clip Index■••[colour: pink][colour: pink][colour: pink][colour: pink][colour: pink][colour: pink]Tilemap Clip Index (0 – 3)
Reserved■[colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: pink][colour: pink][colour: pink][colour: pink]Reserved, must be 0
Layer 2 Clip Index Reset enable■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink][colour: pink][colour: pink]•1 to Reset the Layer 2 Clip Index
Sprites Clip Index Reset enable■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink][colour: pink]•[colour: pink]1 to Reset the Sprites Clip Index
Layer 0/1 Clip Idx Reset enable■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink]•[colour: pink][colour: pink]1 to Reset the ULA/Timex Clip Index
Layer 3 Clip Idx Reset enable■[colour: dark green][colour: dark green][colour: dark green][colour: dark green]•[colour: pink][colour: pink][colour: pink]1 to Reset the Tilemap Clip Index
**NOTE:** This NextREG may change in the future #### NextREG 30 (1Eh) – Active Video Line MSB
Group NameRWData BitsDescriptionHD
76543210
Active Video Line (MSB)■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green]•1 for lines above 255 else 0
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: dark green] 0[colour: pink]Reserved, must be 0
#### NextREG 31 (1Fh) – Active Video Line LSB
Group NameRWData BitsDescriptionHD
76543210
Active Video Line (LSB)■••••••••Active Video Line (LSB)
#### NextREG 32 (20h) – Maskable Interrupt Generation
Group NameRWData BitsDescriptionHD
76543210
CTC■■[colour: pink][colour: pink][colour: dark green][colour: dark green]0000No CTC interrupt generated
[colour: pink][colour: pink][colour: dark green][colour: dark green][colour: pink][colour: pink][colour: pink]•Generate CTC 0 interrupt
[colour: pink][colour: pink][colour: dark green][colour: dark green][colour: pink][colour: pink]•[colour: pink]Generate CTC 1 interrupt
[colour: pink][colour: pink][colour: dark green][colour: dark green][colour: pink]•[colour: pink][colour: pink]Generate CTC 2 interrupt
[colour: pink][colour: pink][colour: dark green][colour: dark green]•[colour: pink][colour: pink][colour: pink]Generate CTC 3 interrupt
Reserved■■[colour: pink][colour: pink][colour: dark green] 0[colour: dark green] 0[colour: pink][colour: pink][colour: pink][colour: pink]Reserved, must be 0
ULA■■[colour: pink]•[colour: dark green][colour: dark green][colour: pink][colour: pink][colour: pink][colour: pink]Generate ULA interrupt
Line■■•[colour: pink][colour: dark green][colour: dark green][colour: pink][colour: pink][colour: pink][colour: pink]Generate Line interrupt
\* Set bits on **R** indicate whether an interrupt occurred or is pending – alias of bits in **NextREGs 200 - 202 (C8h - CAh)**\ \* Set bits on **W** always generate a maskable interrupt ignoring enables – **NextREGs 196 - 198 (C4h - C6h)** #### NextREG 34 (22h) – Line Interrupt Control
Group NameRWData BitsDescriptionHD
76543210
Line Interrupt Value MSB■■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink][colour: pink]•MSB of line number0
Line Interrupt Control■■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink]•[colour: pink]Enable Line Interrupt*0
ULA Interrupt Control■■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green]•[colour: pink][colour: pink]Disable ULA Interrupt*0
Reserved■[colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: pink][colour: pink][colour: pink]Reserved, must be 0
■[colour: light green][colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: dark green] 0[colour: pink][colour: pink][colour: pink]Reserved, must be 0
ULA Interrupt Signal■•[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink][colour: pink][colour: pink]ULA is currently asserting interrupt
\* Aliases of interrupt enable bits in **NextREG 196 (C4h)** #### NextREG 35 (23h) – Line Interrupt Value LSB
Group NameRWData BitsDescriptionHD
76543210
Line Interrupt Value LSB■■••••••••Lower 8-bits of line number0
#### NextREG 36 (24h) – Reserved Protection against **OUT 3Bh, A** – See DISCiPLE disk interface for example.\ In legacy modes set selected **NextREG** to **36 (24h)** #### [?]
Group NameRW76543210DescriptionHD
X Offset■■••••••••8-bit value of X Offset (0-255)0
This setting refers to all ULA modes **except** Layer 1,0 – LoRes\ **NextREG 104 (68h):D2** adds a half pixel to the scroll #### NextREG 39 (27h) – ULA Vertical Scroll Control
Group NameRWData BitsDescriptionHD
76543210
Y Offset■■••••••••8-bit value of Y Offset (0-191)0
This setting refers to all ULA modes **except** Layer 1,0 – LoRes #### NextREG 40 (28h) – Stored Palette Value and PS/2 Keymap Address MSB
Group NameRWData BitsDescriptionHD
76543210
Stored Palette value■••••••••See NextREG 68 (44h)
PS/2 Keymap Address MSB■[colour: pink][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green]•MSB of value in NR 41 (29h)
Keymap Selection■0[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink]Select PS/2 Keymap0
1[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: pink]Select key joystick
Reserved■[colour: pink][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]Reserved, must be 0
#### NextREG 41 (29h) – PS/2 Keymap Address LSB
Group NameRWData BitsDescriptionHD
76543210
PS/2 Keymap Address LSB■••••••••8-bit value (0-255)0
#### NextREG 42 (2Ah) – PS/2 Keymap Data MSB
Group NameRWData BitsDescriptionHD
76543210
PS/2 Keymap Data MSB■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green]•PS/2 Keymap Data MSB*
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: dark green] 0[colour: pink]Reserved, must be 0
\* Not currently used by hardware. Write **0** #### NextREG 43 (2Bh) – PS/2 Keymap Data LSB
Group NameRWData BitsDescriptionHD
76543210
PS/2 Keymap Data LSB■••••••••8-bit value (0-255)
A write causes the data to be written and auto-increments the Keymap Address #### NextREG 44 (2Ch) – DAC B Mirror (Left) / I²S Left Sample MSB
Group NameRWData BitsDescriptionHD
76543210
I²S Left Sample MSB■••••••••8-bit value (0-255)
8-bit sample Left DAC B■••••••••8-bit value*
\* A soft reset sets a value of **128** (**80h**)\ The I²S Left Sample LSB is latched and can be read from **NextREG 45 (2Dh)** later #### NextREG 45 (2Dh) – DAC A+D Mirror (Mono) / I²S Sample LSB
Group NameRWData BitsDescriptionHD
76543210
I²S Last Sample LSB■••••••••8-bit value (0-255)
8-bit sample DACs A + D■••••••••8-bit value*
\* A soft reset sets a value of **128** (**80h**)\ Returns the LSB of last sample read from **NextREG 44(2Ch)** or **NextREG 46(2Eh)** #### NextREG 46 (2Eh) – DAC C Mirror (Right) / I²S Right Sample MSB
Group NameRWData BitsDescriptionHD
76543210
I²S Right Sample MSB■••••••••8-bit value (0-255)
8-bit sample Right DAC C■••••••••8-bit value*
\* A soft reset sets a value of **128** (**80h**)\ The I²S Right Sample LSB is latched and can be read from **NextREG 45 (2Dh)** later #### NextREG 47 (2Fh) – Layer 3 (Tilemap) Horizontal Scroll Control MSB
Group NameRWData BitsDescriptionHD
76543210
Layer 3 X Scroll Offset MSB■■[colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green][colour: dark green]••Tilemap X Scroll Offset MSB0
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
Meaningful range: **0** to **319** in 40 tiles mode, **0** to **639** in 80 tiles mode #### NextREG 48 (30h) – Layer 3 (Tilemap) Horizontal Scroll Control LSB
Group NameRWData BitsDescriptionHD
76543210
X Offset LSB■■••••••••8-bit value (0-255)0
Meaningful range: **0** to **319** in 40 tiles mode, **0** to **639** in 80 tiles mode #### NextREG 49 (31h) – Layer 3 (Tilemap) Vertical Scroll Control
Group NameRWData BitsDescriptionHD
76543210
Y Offset■■••••••••8-bit value (0-255)0
#### NextREG 50 (32h) – Layer 1,0 (LoRes) Horizontal Scroll Control
Group NameRWData BitsDescriptionHD
76543210
X Offset■■••••••••8-bit value of X Offset (0-255)0
Layer 1,0 (LoRes) scrolls in half-pixels at the same resolution and smoothness as Layer 2 #### NextREG 51 (33h) – Layer 1,0 (LoRes) Vertical Scroll Control
Group NameRWData BitsDescriptionHD
76543210
Y Offset■■••••••••8-bit value of Y Offset (0-191)0
Layer 1,0 (LoRes) scrolls in half-pixels at the same resolution and smoothness as Layer 2