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Bit of a dumb question but can I directly interface a 10k10 to a 5v CMOS device or do I need to use pull-ups? From what I can tell it outputs *just* above 3.5v (on a 5v core/IO voltage) so it should be okay, right?
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Direct interfacing should be fine.
Check the data sheet of the device the FPGA interfaces to and see what its input high minimum is. If its less than 3.5V, then you don't need to worry. If it is higher than 3.5V, then you might need to do a little more testing. For example, actually drive the device with an FPGA output and measure the voltage. Worst-case if the device does not recognize 3.5V as a logic high, you would then need to add a pull-up, but you would also have to change your FPGA logic to drive-high and then tri-state (you want to drive high first so that the output gets to 3.5V fast).
Cheers,
Dave
Honored Contributor
