ULA Control Register

From SpecNext official Wiki
Jump to: navigation, search
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

bit 6: 0 to select the ULA colour for blending in SLU modes 6 & 7 (soft reset = 0) 1 to select the ULA/tilemap mix for blending in SLU modes 6 & 7

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)).