Firmware ROMs
-------------

   1818-3133 2238  <-- U510 (85B)/U77/(85C)    <- ROM 1
   1818-1842 2144  <-- U511 (85B)/U79/(85C)    <- ROM 2
   1818-3132 2237  <-- U513 (85B)/U711(85C)    <- ROM 3
   1818-1844 2144  <-- U514 (85B)/U713/(85C)   <- ROM 4
   1818-3134 2238  <-- U75  (85B)/U513/(85C)   <- Boot ROM
   ^ Part no.
             ^ ROM Datecode

   1818-1489       <-- U313 (85B) character rom

Memory map
ROM 1 = 0x0000 to 0x2000
ROM 2 = 0x2000 to 0x4000
ROM 3 = 0x4000 to 0x6000
ROM 4 = 0x8000 to 0x8000

ROM pinout is JEDEC standard 64-kbit (as in the 23C64).

A7  1   24 VCC (+5V)
A6  2   23 A8
A5  3   22 A9
A4  4   21 A12
A3  5   20 CE#
A2  6   19 A10
A1  7   18 A11
A0  8   17 D7
D0  9   16 D6
D1  10  15 D5
D2  11  14 D4
GND 12  13 D3
