Maximum Size of Flash Memory Supported by CycloneIII

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Thank you sir. This point is clear to me.

I want to discuss one more point with you. I want to configure this device with FPGA for general purpose use.

When i run the Memory Test, its give the error, "Flash is not open". Please guide me how can i debug this issue.

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Try debug into library code and find out what exactly generates the error. I guess the Altera HAL driver doesn't support that specific device size; if you are lucky it's simply a matter of adding the device code to the list of supported ones.