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Identify these weird EPROMs

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Alex Eisenhut:
I assume 8331 is the date code of the combined thing, the Fujitsu EPROMs and the MMI PAL. I've seen this type of hybrid approach for "4132" or "4332" 32K x 1 DRAMs (in an Apple II I think?), and of course the kind of cost-is-no-object workstations from the 1980s.

https://www.x86-guide.net/xhoba/en/collection_divers/Dec-VAX-V11-ROM-RAM-chip-cpu-no291.html

But I've never seen something populated with active circuitry top and bottom.

OP, 50$ US + shipping for one?

wraper:
These are not EPROMs but some custom modules consisting of 4 2764 EPROMs and PAL. I really doubt about them working as 27256, you don't need PAL for that.

Benta:

--- Quote from: wraper on February 01, 2023, 02:47:02 pm ---These are not EPROMs but some custom modules consisting of 4 2764 EPROMs and PAL. I really doubt about them working as 27256, you don't need PAL for that.

--- End quote ---
Actually you do need the super-simple PAL for the chip selects. A simple 74xx decoder could probably also have done it, but there was not 100% agreement on the 2764 pinout back then (upper address and VPP). A PAL was safer.

It's "intermediate" 27256 EPROMs from before the real thing became available. Notice how the dies fill the windows completely, meaning it's the maximum die size for the stepper camera and the lead frame.
The "real" 27256s are a couple of geometry shrinks away, probably 2...3 years in those days.
Expensive solution, but apparently necessary.

And extremely cool!  :-+

wraper:

--- Quote from: Benta on February 01, 2023, 08:15:41 pm ---
--- Quote from: wraper on February 01, 2023, 02:47:02 pm ---These are not EPROMs but some custom modules consisting of 4 2764 EPROMs and PAL. I really doubt about them working as 27256, you don't need PAL for that.

--- End quote ---
Actually you do need the super-simple PAL for the chip selects. A simple 74xx decoder could probably also have done it, but there was not 100% agreement on the 2764 pinout back then (upper address and VPP). A PAL was safer.

--- End quote ---
How PAL is supposed to help with Vpp? There is no voltage compatibility. Can you give an example of 2764 with a different pinout? Half of 74LS139 or 74LS138 would do the job.

TheSteve:
I feel like they were probably the worlds first DS/HD (Double Sided High Density) EPROM's.

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