Re: TI-H: Battery question

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Re: TI-H: Battery question

>Mel heres a good one for you... :)

Uhh, okay : :)

>>Thanks for the explanation on VFORWARD...it was very thorough!
>>
>>Another question...
>>
>>How exactly does the Viewscreen work?  I mean, how specifically does each
>>position in the ti's screen get translated to the other screen?

In order to use the viewscreen you must have a special TI-85/82 with
the projector port...  Basically the LCD memory map is copied via the
port directy to the overhead projector every so often, it's probably
interrupt driven (so it's updated like maybe 50 times per second).
This means that 50 times per second the processor is stopped and then
the contents of the vid mem are copied to the projector, where it is
drawn on the screen.  The same happens to the regular LCD, the LCD
controller is constantly reading the video memory in the background
(so it won't screw up the processor accessing the memory, this is
similar to transparent DMA in a PC, quite complicated actually) and
then the LCD is updated accordingly.

This is different from the newer 83 and 86, which use I/O port LCD
controllers.  These don't use a memory map, but instead print pixels
to the screen based on I/O port commands.  I'm not really familiar
with how it is exactly setup, but the controller philosophy itself is
the other main type of controller besides memory mapped.


>>
>>It's also related to the above, but how does an LCD work?  As far as
>>printing a pixel at a specific location?


LCD's utilize horizontal and verticle drivers that combine to "light
up" a particular pixel.  What happens is that when a particular row
and a particular column of the LCD driver is "on", where the row and
column cross is where the pixel will be lit up.  The chemistry of
LCD's is kinda complex, but basically what happens is that when
current flows through it, the crystal effectively aligns and instead
of passing light through the material, it scatters light back in all
directions producing a "black" dot.  Older LCDs did not scatter light
all that well, so you had to look directly perpendicular to the screen
in order to see it.  Newer "supertwist" and nematic displays somewhat
helped the problem, but it's still not perfect.  

-Mel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The TI-Memory Expansion Homepage
-http://www.egr.msu.edu/~tsaimelv/expander.htm
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