I was digging around some more and found
this random pinout reference of a bunch of ROMs used on a bunch of random arcade boards. Most of them are similar to the JEDEC standard pinout, but this is conspicuously different:
Code:
(4M) 512k x 8 mask rom
HN62304
A8 1 +-v-+ 32 A9
A7 2 | | 31 A10
A6 3 | | 30 A11
A5 4 | | 29 A12
A4 5 | | 28 A13
A3 6 | | 27 A14
A2 7 | | 26 A15
A1 8 | | 25 A16
oe? 9 | | 24 A17
gnd 10 | | 23 A18
ce? 11 | | 22 gnd
D0 12 | | 21 A0
D1 13 | | 20 D7
D2 14 | | 19 D6
D3 15 | | 18 D5
+5v 16 +---+ 17 D4
I find it amusing that this is clearly a 16-bit ROM where they've just chosen to not wire bond D8-D14, and wire bonded /BYTE to ground internally.