I have a design which was originally for an EP4CE40F23, and now I want to migrate to EP4CE55F23. I can compile the design correctly (i.e. I am not having used any I/O pins which are not available in the larger device).
However, my existing boards have these pins unconnected and not connected to VCC/VCCINT/GND etc. Does the larger device still works on the board (i.e. because its power pins are internally connected) or do I need to redesign the board to have the supply on ALL these pins?
Are you sure the pins are not tied together internally? For Xilinx devices, that seems to be the case:
I have verified and the power pins in the EP4CE55F23 are internally tied together. I have soldered one device on a board designed for a EP4CE40F23 and confirmed it's fully working! (It's not good practice, though. I think I'm going to make a redesign of the board which feeds all power pins, though. This is also what the "Migration Assistant" yields as connections, if you select EP4CE40F23 as base device and EP4CE55F23 as migration device).
I would never leave power or ground pins unconnected. You will have more switching noise on the chip, which may cause malfunctions which you will have to explain to your boss.
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