I can't get me hands on a 27C020 for a few weeks, but I do have some 27C4001 EPROM's that have been uv erased. I have an EPROM burner (willem universal), however, I not sure if I can use the 27C4001 as it is 512k as opposed to
256k. I guess if I duplicate the data over the two halves of the chip, then it should be okay?
That would work, but it is not needed. The 27C4001 has one more address line. In your application circuit, if you keep that extra address line tied to gnd, you only need the first half of it to be meaningful. The first half is the range of addresses you span by keeping the most significant address bit equal to 0, during programming.
Best.
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