http://forums.nesdev.com/viewtopic.php?f=9&t=15915&p=195252&hilit=prg#p195252
255 in 1
Bus conflicts: no
All bits of REG are set to 0 on power up & reset
REG: $8000-$ffff
A~[1xxx xxxx xxPP PPPv] D~[xCCC CCCm]
|| |||| ||| ||||
|| |||| ||| |||+- mirroring (0: V, 1: H)
|| |||| +++-+++-- 8 kiB CHR-ROM bank at $0000-$1fff
|| |||+--------------- PRG-MODE (0: 16 kB, 1: 32 kB)
++-+++---------------- PRG-ROM bank at $8000-$ffff
v|$8000-$bfff|$c000-$ffff
-+-----------+-----------
0| PPPPP | PPPPP
1|
-------------------------