OCS/ECS-only "7-plane" mode.
If BPLCON0 is set to 7 planes following interesting things happen:
- Agnus DMA sequencer uses 4 planes mode
- Denise shows all 6 planes (can be EHB,HAM or DPF, all work)
BPL5DAT and BPL6DAT are "static" (16-bit pattern repeats) 5th and 6th plane pattern. (of course copper can also be used to update the pattern)
This trick was used in intro First Anniversary by Lazy Bones (perhaps only one program using it..) BPL5DAT was used for vertical lines. Normally you can't have >4 planes without slowing down the copper.
Perhaps it can also be used for some weird EHB/HAM tricks
