ULA Control Register
|Short Description||Disable ULA, controls ULA mixing/blending, enable ULA+|
|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||since core3.1.4: Cancel entries in 8x5 matrix for extended keys|
|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 Control Register ($15)).