GLCD library on arduino due

The released glcd s/w currently is tied to AVR.
Currently to get the desired speed and minimum delays, the library
uses AVR port i/o and inserts AVR specific opcodes to generate cycle accurate delays.
At some point I'll add support for a generic "Arduino" i/o mode that will use Arduino core code
routines when direct port i/o capabilities are not available.
(I already helped a guy get an experimental version of glcd going on a chipkit pic32 based board.)

The biggest issue that will make it more difficult for DUE is actually the DUE hardware.
The DUE is not 5v tolerant. This means that displays like the ks0108 cannot be directly
connected to the DUE pins. The glcd typically needs a source voltage of around 4.5 to 5 volts
which will mean that it will drive signals at that level which is too much for the DUE inputs.

A generic i/o mode "just works" for boards like the chipkit boards since the pic32 processor is 5v tolerant
and can be wired directly the glcd.
When I get to it, I'll be testing out the generic mode on the chipkit UNO32 first as that is the hardware I have
and it is 5v Tolerant.

For a DUE it would also need some sort of level shifter circuitry between the glcd
and the DUE to map the voltages for the DUE.
It can be done but it definitely isn't as easy as hooking up wires
like with the AVR or pic32 based boards.
The issue is many of the signal lines (8 data lines) are bi-directional. I'm guessing that trying to get
away with using resistors rather than true bi-directional level shifters will have issues for those signals.
Adafruit sells an 8 channel bi-directional level shifter module for about $8 that might work.
I've not taken any time to see what might actually be possible.

Interfacing to 5v logic is more difficult with DUE than the chipkit boards.

--- bill

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