I bet it's a relatively ordinary
pinout...probably the ROM version
of a 2716 or 2732. I believe those chips have part numbers like
"2316" and such, if memory serves. There were lots of mask ROMs that
were pin-compatible with EPROMs in that era, before one-time
programmable EPROMs (plain EPROMs but in plastic packages with no
erasure window) became cost-effective.
Are the numbers on your chip readable? If so, what are they?
They arent anything obvious, thats the deal...
AMI 8147BXW (date code...8147...?)
CO12406-01 (your guess...)
(c) 1980 Atari
Korea
I am suspecting a 2716 or 2732 too but...
...
Claude