Kiosk board (eccc 2009) layout
-------------------------------------------
     h         [0 rom] [a5] [b5] [c5]
     e                 [a4] [b4] [c4]
     a         [u1]    [a3] [b3] [c3]
     d         [u2]    [a2] [b2] [c2]
     e       [u3]      [a1] [b1] [c1]
     r     [u4] [u5]
           [u6] [u7]


                    [expansion port]

rom, a-c/1-5 = 27c256 eprom

U1,2,3 = 74ls138
U4,5   = 74ls174
u6     = 74ls123
u7     = 74ls00