Spartan3 Live Insertion with XC9572XL chip

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Hi everyone, Ive got some questions about live insertion of S3 chips.

I am designing an fpga module as well as a daughterboard that will
receive the module.

The main system contains an XC3S200 and is connected straight to
headers on the board.
Now the secondary board contains an XC9572XL cpld and connects to the
XC3S200 directly through the headers.

The main board as well as the daughter board contain their own power
supply with shared ground. The way the boards are powered on and the
order in which they are is totally arbitrary. The secondary board could
be powered up and the main module not and it would be eventually
plugged in or the main module could be on and vice versa.

Would the procedures said above affect the S3 in terms of internal
damages. AFAIK, there are clamp diodes on the IOs of the S3 that
prevent their Vout/Vin voltage to go beyond their operating forward
voltage + VccIO of the S3. Now, would this protect my chip if excessive
voltage is applied to the IOs during an off state (no voltage is
applied to my Vccint, Vccio, Vccaux of S3); that is, if the cpld is on
and outputing 3.3V and my S3 is off... What will happen if also, my
cpld is on and outputing 3.3V and my S3 is on and placing zeros on its
outputs (in this case, i think a series resistor of 100ohm would take
care of the excessive current).

Thanks for any pointers
JLA


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