ULA Control Register
From SpecNext official Wiki
| Number | $68 |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Disable ULA, controls ULA mixing/blending, enable ULA+ |
| Bit | Function |
|---|---|
| 7 | 1 to disable ULA output (soft reset = 0) |
| 6-5 | since core3.1.1: Blending in SLU modes 6 & 7 (soft reset = 0)
= 00 for ULA as blend colour = 10 for ULA/tilemap as blend colour = 11 for tilemap as blend colour = 01 for no blending
|
| 4 | Reserved, must be 0 |
| 3 | ULA+ enable (soft reset = 0) |
| 2 | may change (ULA half pixel scroll) (soft reset = 0) |
| 1 | Reserved, must be 0 |
| 0 | 1 to enable stencil mode when both the ULA and tilemap are enabled
(if either are transparent the result is transparent otherwise the result is a logical AND of both colours) |
Bit 0 can be set to choose stencil mode for the combined output of the ULA and Tilemap.
Bits 6-5 determine what colour is used in SLU modes 6 & 7 where the ULA is combined with Layer 2 to generate highlighting effects (Sprite and Layers System Register ($15)).