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Bizarre Xilinx configuration problem

Bringing up a new FPGA board I have encountered a very bizarre problem:

If I enable a specific pin as an output, the FPGA fails to configure.

This pin can be grounded, tied high, or used as an input without problem so its not the state of the pin that matters, but how it is connected inside the FPGA. Just making it an output (even if tristated and never enabled) will make configuration fail.

Details:

Part is Spartan3 XC3S400-TQ144

Pin that cannot be an output is pin 12

Two cards/FPGA chips have identical problem

Parallel config method

FPGA configuration fails with /INIT and DONE low - as if a CRC error occured

If I assign the output that would go to pin 12 elsewhere, there is no problem and everything else works, including all the other pins in the same I/O bank as pin 12.

Has anyone ever seen anything like this? -- pulling out what left of my hair trying to see how this could happen...

Peter Wallace

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Peter C. Wallace
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Peter,

Have you checked that this pin is not a dual use pin (also used for configuration)?

Austin

Reply to
austin

No, its just a regular pin (which is why we were so confused that it mattered), BUT Looks like its a problem with our USB configurator, We hacked our configurator CPLD so we could configure via a parallel port and that works fine. Must be we are corrupting the last few bytes of configuration data somehow. Sorry for the trouble.

Peter Wallace

Reply to
Peter C. Wallace

Peter,

Asking weird questions about FPGAs means you never have to say you are "sorry."

Goes with the territory.

Aust> >

Reply to
austin

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