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At first glance it looks like Devil Zone (Universal Board #8022) is *almost* identical to No Man's Land (#8003) and Magical Spot (#8013).
It's got the same hideous #8013-V1 hack daughterboard from Magical Spot, and its own sound and aux gfx boads.
The one change I do see is the priority in the final gfx mux. The mux inputs are the same on both, but the mux select decodes are different.
On NML, the aux board bit comes into D6, and forces the mux selects both high to give the bits from the aux highest priority.
Priority doesn't really matter here since the code doesn't let you drive/shoot through the trees,
On Devil zone, the mux selects don't care about the aux board data.
The logic is a bit goofy since they were reworking existing hardware, but it works out as
MuxB (pin 3) is now ~Video1 || ~CSEL2
MuxA (pin 8) is now CSEL2
When CSEL2 is low (either sprite bit plane set), we get 01, selecting the CRL sprite colors.
When CSEL2 is high and VIDEO1 is high (no sprite, BG on), we get 10, selecting the BG color bits from the D2 PROM.
When CSEL2 is high and VIDEO1 is low (no sprite or BG data), set get 11, selecting the aux board colors, giving them the lowest priority.
There's no 00 decode for black here, but when everything is off we still get black.
Since the priority matters on Devil Zone (blue lines over other graphics would look dumb), but not on No Man's Land (sprites are never drawn over the water/trees) or Magical Spot (no aux gfx board), it makes sense to mod the design for this priority scheme instead (and to redo the 4-NAND mess above to free up some gates.
It's got the same hideous #8013-V1 hack daughterboard from Magical Spot, and its own sound and aux gfx boads.
The one change I do see is the priority in the final gfx mux. The mux inputs are the same on both, but the mux select decodes are different.
Code:
BA Input
00 Black
01 Background
10 Sprites (CRL)
11 Aux Gfx (CRT)On NML, the aux board bit comes into D6, and forces the mux selects both high to give the bits from the aux highest priority.
Priority doesn't really matter here since the code doesn't let you drive/shoot through the trees,
On Devil zone, the mux selects don't care about the aux board data.
The logic is a bit goofy since they were reworking existing hardware, but it works out as
MuxB (pin 3) is now ~Video1 || ~CSEL2
MuxA (pin 8) is now CSEL2
When CSEL2 is low (either sprite bit plane set), we get 01, selecting the CRL sprite colors.
When CSEL2 is high and VIDEO1 is high (no sprite, BG on), we get 10, selecting the BG color bits from the D2 PROM.
When CSEL2 is high and VIDEO1 is low (no sprite or BG data), set get 11, selecting the aux board colors, giving them the lowest priority.
There's no 00 decode for black here, but when everything is off we still get black.
Since the priority matters on Devil Zone (blue lines over other graphics would look dumb), but not on No Man's Land (sprites are never drawn over the water/trees) or Magical Spot (no aux gfx board), it makes sense to mod the design for this priority scheme instead (and to redo the 4-NAND mess above to free up some gates.