--- Quote Start ---
Setting pins connected to other chips to tristate isn't a good idea, because the pins float to an unknown value, vcc or gnd is even worse, because you have to assure, that no pin is driving out, possibly damaging a FPGA pin by a high short circuit current. You should select either tristate with weak pull-up or hold-circuit for unconfigured pins.
As said, there's no simple explanation for the observed behaviour. It may be the case, that a floating tri-state pin enabled the connected device in an unexpected way and caused switching noise affecting other parts of the circuit. Also a high current consumption can overload the power supply in this situation.
--- Quote End ---
It Worked :), thanks a-lot for the help.
as for your interest, i had following findings
well the output results were the same when set to "tri-state with weak pull-up" (i.e. everything still not working),
but every thing get normal when i changed it to "as input tristate with bus hold circuit" now the core is working as it should !!!
thanks,
regards.
Honored Contributor
