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cbrues
Member Since: May 20, 2011
Country: United States
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I realized I was looking at the schematic on the Alchitry website, which is for the old version of the board. However, on the new Sparkfun version, the pulldowns for the pushbuttons are in the wrong part of the circuit, and don't actually pull down the FPGA pin.
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The push buttons and dip switches on the Io board aren't compatible with the Cu main board when stacked directly. The Io board switches and buttons connect the FPGA pin to VCC (through a resistor). The ice40 on the Cu main board doesn't have a pulldown option for the I/O buffer. Therefor, the state of the FPGA pins is either VCC or floating.
There is a post on the Alchitry forums about this and they recommend swapping the pin between output low and input right before sampling it and hint that it might be fixed in a future revision.
Another option is to use a Br board and some pulldown resistors, but it would be hard to fit them for all of the dip switches.
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Just a note, the E-Textile Basics link in the Documents section doesn't work.
No public wish lists :(