On Thu, May 28, 1998 at 06:22:16PM -0700, Tim May wrote:
ROMs currently have no sensitivity to cosmic rays or alpha particles from natural radioactivity in the environment, and are not expected to. Single event upsets typically happen with cross-coupled static RAM cells or with dynamic RAMs. _Some_ errors happen in logic circuits, including microprocessors, but not many.
No doubt some examples of reported errors in ROM circuits can be found, but I suspect the errors are either in the decode logic or elsewhere, and certainly not in the mask-programmable bits or the blown fuse sections. Lots of ROM types exist, so I don't want to try to list all major types here.
Some EAROMs (Electrically Alterable) or EEPROMs (Electrically Erasable) are sensitive to some radiation events, but not nearly as sensitive as RAM chips are. The IEEE Transactions on Nuclear Science, the December issue of every year, is devoted to reporting on actual sensitivity levels and physical mechanisms.
I certainly defer to your expertise, as I have no particular knowlage of radiation effects aside from reading an occasional technical paper or article touching on the subject tangentially. What I should have said in any case is damage to Flash EPROM or other electrically programmed EPROM, as several people have pointed out that fuse and mask programmed ROMs are not at all subject to single event radiation damage. I suppose that ROMs on board a satellite could easily afford to be masked types, but of course there still are sound engineering reasons to keep ROM'd code as minimal, simple and straighforward as possible, especially when it cannot ever be changed and hundreds of millions of dollars of satellite depends on it. -- Dave Emery N1PRE, die@die.com DIE Consulting, Weston, Mass. PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18