| Bits | Description |
|---|---|
| 7 | Place AY 2 in mono mode (hard reset = 0) |
| 6 | Place AY 1 in mono mode (hard reset = 0) |
| 5 | Place AY 0 in mono mode (hard reset = 0) |
| 4 | Sprite id lockstep (nextreg 0x34 and port 0x303B are in lockstep) (soft reset = 0) |
| 3 | Reset divmmc mapram bit (port 0xe3 bit 6) (read returns 0) |
| 2 | 1 to silence hdmi audio (hard reset = 0) |
| 1:0 | Scanline weight 00 = scanlines off 01 = scanlines 50% 10 = scanlines 25% 11 = scanlines 12.5% |