21MX proms (per request)

[Jon Elson]

On 09/07/2015 12:47 PM, Sean Caron wrote:
> But I do think there's merit in Alexandre's general argument that one could
> theoretically emulate the older bipolar PROMs with some mix of modern
> components ... and the programmable device would be (a) more easily
> obtainable than the old bipolar PROMs and (b) programmable with
> inexpensive, contemporary USB device programmers which are definitely big
> positives.
>
>
Most likely, one could use a parallel modern EPROM that is 
as fast as the old bipolar PROM.
Of course, the pinout would be totally different, probably 
in a larger size package with way more pins.

This one is 256K and 70 ns access time.
http://www.digikey.com/product-detail/en/AT28HC256-70JU/AT28HC256-70JU-ND/2050794

If you REALLY need it fast, Winbond has a 45 ns EPROM, but 
not in stock at Digi-Key.
That's their W27C512-45Z

Jon