Difference between revisions of "Sprite port-mirror Index Register"
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(Core 2.00.22 changes, and forum knowledge from Jim Bagley distilled.) |
(Core 2.00.23 changes (sprite-index link with port $303B)) |
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| Line 3: | Line 3: | ||
|Readable=Yes | |Readable=Yes | ||
|Writable=Yes | |Writable=Yes | ||
| − | |ShortDesc=Selects sprite index 0..63 to be affected by writes to other Sprite | + | |ShortDesc=Selects sprite index 0..63 to be affected by writes to other Sprite ports (and mirrors). |
}} | }} | ||
| − | + | {|class="wikitable" | |
| + | ! Bit !! Description | ||
| + | |- | ||
| + | | 7 || Enable "link" with I/O port {{PortNo|$303B}} (sprite index for port {{PortNo|$xx57}}) (1 = interlinked, 0 = decoupled) | ||
| + | |- | ||
| + | | 6 || reserved, write 0 | ||
| + | |- | ||
| + | | 5-0 || Sprite index (0..63), which sprite-attributes will be modified. | ||
| + | |} | ||
| + | When the index is "linked" (bit 7 is set), it ties the nextreg sprite-index and the I/O sprite-index together. | ||
| + | * any change to the nextreg sprite number via write to nextreg $34 or auto-inc on nextreg $75-$79 will set the sprite index for I/O to the same and also reset the I/O attribute port {{PortNo|$xx57}} (next write to sprite-attribute port will modify first byte of attributes of particular sprite) | ||
| + | * any change to sprite number via I/O port {{PortNo|$303B}} or auto-inc via I/O port $xx57 will also be reflected in nextreg $34. | ||
| + | |||
| + | This link is broken by writing to nextreg $34 with bit 7 reset. | ||
Revision as of 17:20, 28 December 2018
| Number | $34 |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Selects sprite index 0..63 to be affected by writes to other Sprite ports (and mirrors). |
| Bit | Description |
|---|---|
| 7 | Enable "link" with I/O port Sprite Status/Slot Select ($303B / 12347) (sprite index for port Sprite Attribute Upload ($xx57 / 87)) (1 = interlinked, 0 = decoupled) |
| 6 | reserved, write 0 |
| 5-0 | Sprite index (0..63), which sprite-attributes will be modified. |
When the index is "linked" (bit 7 is set), it ties the nextreg sprite-index and the I/O sprite-index together.
- any change to the nextreg sprite number via write to nextreg $34 or auto-inc on nextreg $75-$79 will set the sprite index for I/O to the same and also reset the I/O attribute port Sprite Attribute Upload ($xx57 / 87) (next write to sprite-attribute port will modify first byte of attributes of particular sprite)
- any change to sprite number via I/O port Sprite Status/Slot Select ($303B / 12347) or auto-inc via I/O port $xx57 will also be reflected in nextreg $34.
This link is broken by writing to nextreg $34 with bit 7 reset.