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The Raspberry Pi Compute Module Development Kit Quick Start Guide says that prior to using the kit, the IO bank voltage jumpers (which power the GPIO banks) should be checked. However, I can find no reference that tells how to check them -- from looking at the schematic, it appears that they select between 3.3V and 1.8V

How do you determine which is the correct voltage to use? Is it just a matter of "you'll know it when you need it and until then, pick one"?

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    I can't find an answer either. It seems you can choose. I suppose 3V3 would be potentially faster than 1V8. Perhaps it depends on whether you are going to connect 3V3 or 1V8 devices to the gpios?
    – joan
    Commented Apr 21, 2015 at 10:24
  • @joan -- that's what I'm suspecting: once the user decides how the real world is going to interact with board, the choice will be obvious. It's just that the docs made such a big deal of being sure to check it before powering on for the first time (but it's not like you're going to order one of these and immediately connect it to peripheral hardware before you actually try to install software on it).
    – jhfrontz
    Commented Apr 21, 2015 at 14:49
  • I think they are trying to stress you must have a jumper in place - it doesn't matter if it's 3V3 or 1V8. With no jumper you can harm the compute module if you power it up.
    – joan
    Commented Apr 21, 2015 at 14:55
  • @joan ah, that makes sense; tnx!
    – jhfrontz
    Commented Apr 21, 2015 at 14:57
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    @joan You should probably include that as an answer so this question can be marked complete.
    – Josh Burgess
    Commented Apr 28, 2015 at 3:22

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It is a matter purely of how you wish to use the device, and i believe that the jumper position selection should be based on the power requirements of the devices(s) being connected to the module. The manual you referenced seemed to place stress on ensuring that you have a jumper in place and not which position it is it. Based on personal experience i would believe this is because they are probably receiving many support calls due to the jumper not being inserted.

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