What to do with (currently) unused I/O?

[MartyMacGyver]

If I program my Papilio Pro + LogicStart to only use the LEDs and switches (leaving everything else unused and omitted from the UCF per other advice here) I notice that all segments of the 7-segment displays glow dimly once it's programmed and active.

 

I wonder: would it be better to set all unused I/O lines to high-impedance to prevent this side-effect - or is that already the default, and I need to choose something else as a default?

 

Or, is this actually a sign of some physical problem? The board looks OK... Since I've been doing more reading than programming and I'm waiting on a new joystick cap I haven't fiddled with the 7-segment displays yet.

[hamster]

This isn't a problem - the outputs are in a High-Z mode, but still a little current can be sourced/sunk through the I/O pin. 

 

The default setting for unused pins can be set in the tools - I think it is a property of the "Generate Bitstream" process.

[Jack Gassett]

Marty,

 

You could also enable a pull down resistor on those pins which I think should stop the phantom flickering.

 

Jack.

[MartyMacGyver]

Thanks! Would "pulldowns all around" be reasonable for this board, when it comes to unused inputs?

 

Yes, I'm recently aware of the unused pin property, but I'm not sure what's optimal. As a more general rule for unconnected I/O, would pulldowns be optimal, or would high-Z be (in terms of reducing noise and not consuming more power than is absolutely necessary due to unused pins)?

[hamster]

IIRC, you might actually need pull-ups on the anode pins - they are "active low".