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Observer mat01
Registered: ‎05-04-2009

Spartan3A configure from PROM problem



I'm experiencing problems with a new board, the Spartan XC3S200A is not configured by the XCF02S PROM. I'm not completely new to this so I think I did the PROM file and the programming correctly but last time I had to get a similar cuircuit up and running was a few years ago. The FPGA can be programmed in IMPACT and then runs as expected but it isn't loaded on startup by the PROM obviously. The first thing I checked and found strange is that the Mode[0:2] Pins have HIGH level although open at the moment. They should be all '0' to load from that PROM right ? The regarding pins are used as outputs later on but I even removed that from the design. Later they will be connected so some driver IC but it isn't soldered yet so they're open. So why could they be high ? They're also read as '1' when reading the status register. 

Does anyone have an idea ?

Thank you very much for every hint,


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Observer mat01
Registered: ‎05-04-2009

Re: Spartan3A configure from PROM problem

I forgot to mention in my original post that I also tied the Mode pins to GND with some small resistors (33R) and still got the ones when reading status and strangely the HIGH level when measuring the pins. In the meantime I tried connecting them directly to GND and now the FPGA is actually loaded on startup, while when reading the status the pins are still read as '1'. What is that about ? I mean these pins are supposed to be shared config pins and user-ios. But if even a small resistor causes them to fail then one can't use them. Has anyone an idea what goes wrong here ?
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