07 = all outputs de-asserted
04 = 1K RAM enabled
02 = PROM starting at E000 enabled
0E = PROM starting at C000 enabled
0A = BOTH C000 and E000 PROM enabled (during Phantom)
05 = RAM enabled for write (during Phantom when at 0000)

Outputs:

8's bit = C000=CFFF PROM enable (active high)
4's bit = E000-FFFF PROM enable (active low)
2's bit = 1K RAM enabled (active low)
1's bit = Board select (active low)