I had someone ask me a question that I need to refer on to the EEs.
In the Butterfly, the LCD segment pins are shared with general I/O port pins, but the LCD is hard wired in place. Lots of people, myself included, use the general I/O ports and ignore the random LCD segment activity that accompanies such use.
However, the questioner points out you're not supposed to apply a DC voltage to an LCD. The datasheet says:
The voltage must alternate to avoid an electrophoresis effect in the liquid crystal, which degrades the display. Hence the waveform across a segment must not have a DC component.
The datasheet elsewhere mentions that those segment pins that are not used to drive LCD segments may be used for general I/O and doesn't address the specific question at that point. But later (under the "Disabling the LCD") the datasheet says:
When the LCD is disabled, port function is activated again. Therefore, the user must check that port pins connected to a LCD terminal are either tri-state or output low (sink).
This would imply one should not output a high onto any of the Butterfly's segment pins, even when the LCD backplanes, etc., haven't been enabled.
In the particular case under discussion, the LCD's segment pin is used in LED multiplexing and is being driven low (optionally) for 1 ms then high for 3 ms. The solution in this case is to switch to input (tri-state) rather than driving it high, but the general question remains.
Comments? Any insights greatly appreciated.