Do old FPGA's decay?

Peter C. Wallace pcw at
Thu Dec 1 09:20:49 CST 2005

On Thu, 1 Dec 2005, Chuck Guzis wrote:

> I found why my PCTD 3 tape controller was defying my attempts to probe
> it--the XC2064-50 FPGA seems to be dead as a doornail.  Regardless of
> signal inputs, it remains stubbornly inactive--i.e., my logic analyzer says
> that none of the identifiable outputs changes state.
> Since DMA and interrupt logic (as well as configuration) is contained in
> the FPGA, attempting to read from any I/O port returned FF.  A jumper
> bypassing the FPGA for IO read, shows that the drive status lines are
> indeed present and readable.  Similarly, writing to the appropriate I/O
> address causes the expected drive line to wiggle.
> Since I don't need soft configurability (only for IRQ and DMA; the I/O
> address is set via DIP switch), I may remove the FPGA and substitute some
> TTL.  I haven't decided yet.
> But do old FPGA's just quietly go belly-up?  Or is there something about
> the XC2064-50 that I'm in the dark about?  Are there any easy tests that I
> can apply to confirm my suspicions?
> Cheers,
> Chuck

XC2064a are SRAM based FPGAs and _are_ inactive until their configuration is 
loaded, Thats what I would check into... (configuration loading)

Peter Wallace

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