Rochester, 26 juni 2006.

Dear Janko,

You're going to have fun with this one :). Let me give you an impression on
each step:

1) Read data from the SDcard. I believe an SDcard has an SPI interface, so
with 3 wires and some power connections, and the correct implementation of
the protocol, you should be able to read word x at address y from the
device. Note that SDcards run at 3.3V, and are not 5V tolerant, in general.
Therefore, you will need to either run your PIC at 3.3V (meaning you can't
get above an 8 MHz clock) or you need to use a resistor network. Note that
there are PIC with built in SPI hardware, which will allow you to
communicate with the SDcard at a much faster rate.

2) You need to find the text file in the memory of the SDcard. Obviously
this depends on how the SDcard is formatted, but it is most likely one of
the FATxx systems. You will have to implement this file system to a certain
extend in order to find the text file, or make sure the text files fits in
one allocation unit, and have a unique identifying sequence in it, so you
can just run through the entire memory to find them.

3) Displaying things on a graphic LCD. This depends on the type of display,
but there are a few things to note:
3a) Graphic LCD need a fair amount of pins connected in order to work. They
rarely have defined time limits, and benefit from using a two way interface.
The average number of pins you will need is 12 +/- 1.
3b) Not all graphic LCD have a built in font. I recommend getting one with a
built in font, because if there isn't one, you will have to manually
generate all the characters from the text file on the display.
3c) Initialisation of character LCD are well known. For graphic LCD it is
more tricky, and can depend on the size of their internal memory, the speed
of their controller and various other circumstances.
3d) Almost all graphic LCD I came across require a negative driver voltage,
of about -10V or more. Getting this voltage, especially if you run at 3.3V,
might take some charge pump circuitry. In theory a PIC can do this using
PWM, though I never tried this myself.

I deliberately split this up into three steps. I sincerely recommend, since
you state to be new to PICs, to at least do steps 1 and 3 completely
separate from your project first (so write a program that can read value x
from address y of the SDcard, and write a separate program that can write
"Hello World!" on a graphic LCD). Step 2 depends on your programming
experience outside of PIC, as implementing file systems is something that
can be done on any processor, with PIC only adding minor complications.

Greetings,
Maarten Hofman.
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