Configuring 2 Cyclone III's from one EPCS16 Using 2.5V

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I cannot program the two FPGA's separately since I cannot decouple the Config_Done's.

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You misunderstand. The first FPGA *can* be configured by the EPCS device, but it will not enter user mode, since the other device is holding CONF_DONE low.

If you use JTAG to program the second device, then it will release CONF_DONE, and both FPGAs should enter user mode.

Yeah, its subtle, but it should work.

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However, if I repeatedly trigger off of nCEO and monitor Config_Done at 10 mV per division and lots of averaging I can tell that the first FPGA must have

released its Config_Done right at the time that nCEO goes active (low). Config_Done shows ringing and a 3 mV change in its level.

This looks like evidence that it is the second FPGA that is failing its configuration, yes ??

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Yeah, that sounds like a reasonable assumption.

You did not comment yet whether you can program these devices with JTAG.

Cheers,

Dave