u1:o0 -> r0 :oe
u1:o1 -> ra4:oe
u1:o2 -> rb4:oe
u1:o3 -> ra5:oe
u1:04 -> rc4:oe
u1:o5 -> ra3:cs
u1:o6 -> rb3:cs
u1:o7 -> rc3:cs

u2:o0 -> rb5:cs
u2:o1 -> rc2:cs
u2:o2 -> rb2:cs
u2:o3 -> ra2:cs
u2:o4 -> ra1:cs
u2:o5 -> rb1:cs
u2:o6 -> rc5:cs
u2:o7 -> rc1:cs


u3:o0 -> u1:e1
u3:o1 -> u2:e1
u3:o2-o7 -> expansion
u3 always selected


u1+u2 selected by /ROML

u3:  a0 -> u4:q5 -> [Q] ->
     a1 -> u4:q4 -> [Q] ->
     a2 -> u4:q3 -> [Q] ->

* write bits to u4 [xxxx] to select a bank of 8 roms.

u1+2:a0 -> u5:q5 -> [Q] ->
     a1 -> u5:q4 -> [Q] ->
     a2 -> u5:q3 -> [Q] ->

* write bits to u5 [xxxx] to select a rom within the current bank.

==ROMS==
A15 -> [solder pads] {default vcc} [option: u4:q0]
A14 -> u4:q1
A13 -> [solder pads] {default u5:q1} [option: c64:a13]
A12-0 -> c64:a13-0 (assumed)

==LATCHES==

U5:D2 -> C64:D5
U5:Q2 -> c64:/exrom
u5:D3 -> c64:a0
U5:D4 -> C64:A1
U5:D5 -> C64:A2

U4:D0 -> C64:D2
U4:D1 -> C64:D1
U4:D3 -> C64:A5
U4:D4 -> C64:A4
U4:D5 -> C64:A3

U5:D1 -> C64:D0