The first step to explore the ROM is to read it. As it turned out it was really easy and read just fine with the "NEC UPD27C4001 @ DIP32" chip selected in the software of my programmer.
Removed ROM:
ROM in programmer:
To find out if the data i read is good (because i dont know if the "user definable" pins are configured right on the D23C4001E) i just wrote a 1:1 copy of the data to a AM27C040 IC (same as 27C4001).
And yes. It works completely normal with a self written ROM. HUGE SUCCESS.
The next step is to have a closer look at the content of the ROM...
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