On Fri, Sep 11, 2015 at 12:41 PM, GerardCJAT <gerardc...@free.fr> wrote: > HOW OFTEN theses old PROM fail ??
Note that some bipolar PROMs suffer from fuse regrowth, where bits that have been programmed gradually revert to an unprogrammed state. This was a big problem with NiCr fuses. Later bipolar PROMs used different fuse materials; TiW was one of the later choices. I don't know whether TiW or other newer fuses have regrowth issues, but if they do, it's slower than NiCr. It is possible to recover the bits from a bipolar PROM with regrowth by decap and optical inspection, because the regrowth happens in relatively narrow tendrils which are visibly different than an unprogrammed fuse. I've actually seen that done. There is speculation that it could be done without decap by trying to blow each unblown fuse and measuring the energy required to blow the fuse; a regrown one should require less energy. I'm not aware of anyone actually having done it that way. I wouldn't trust a one-of-a-kind PROM to that process. Obviously it's best to dump the PROM contents before regrowth becomes an issue.
