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forgot to save the readme before checking in

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dwelch67
2014-12-17 00:26:40 -05:00
parent 71b4233a6f
commit 9e8292b299
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4
README
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@@ -5,8 +5,8 @@ whatever your term is for this.
I am in no way shape or form associated with the raspberry pi organization
nor broadcom. I just happen to own one (some) and am sharing my
experiences. The raspberry pi is about education, and I feel low
level education is just as important as Python programming.
experiences. The raspberry pi is about education, and I feel bare
metal education is just as important as Python programming.
From what we know so far there is a gpu on chip which:

62
spi03/README
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@@ -17,7 +17,13 @@ http://www.adafruit.com/products/338
I got 5 of them on ebay for $13 with pins.
Perhaps some soldering is required, in some way you need to hook up
the signals.
the signals. Note both above and below the display you might have a
row of pins on your board. They are probably the same and you probably
only need to hook up to one of the two. Also note that the metal frame
has a thick side and the rest are thin, that thick side is normally the
TOP of the display or at least for this example it is. You will note
in the sparkfun and adafruit photos their examples also have the thick
side up.
I use these, but bought the 100 pack
@@ -61,11 +67,53 @@ are the same you only need one row.
The various examples out there use the same init routine.
spi_command(0x21); //extended commands/horiz addressing/chip active
spi_command(0xB0); //vop
spi_command(0x04); //temp coef
spi_command(0x14); //bias mode 1:48
spi_command(0x20); //extended off/horizontal addressing, chip active
spi_command(0x0C); //display on
So that set for horizontal addressing. The display I bought on ebay
said 84x84 but it is really 84x48 pixels, obviously a typo or maybe
trying to sucker me in. Doesnt matter wasnt holding my breath for a
bigger display. First lets set the address pointer to the top left
spi_command(0x80); //column left
spi_command(0x40); //row top
then if we just blast some bytes out start with a smaller number
for(ra=0;ra<32;ra++) spi_data(ra);
you will see they swipe across the top left to right. Each 8 bits
draws a column with those 8 bits with the lsbit being on the top, this
is also shown in the PCD8544 controller document that describes how
to program this thing.
and if you say write 100 bytes then after the 84th byte it
drops down and writes the next 8 rows of pixels and so on.
so 84*48 = 4032 pixels 4032 / 8 = 504 so if we write 504
bytes in theory we cover the screen.
for(ra=0;ra<504;ra++) spi_data(ra);
and that does work.
so call it dumb luck or divine intervention or whatever the font
data orientation from my prior spi02 example happens to already be
lined up just right for this example...Didnt have to flip or rotate
or anything. A little experimenting here:
spi_command(0x80); //column
spi_command(0x40); //row
for(ra=0;ra<10;ra++)
{
for(rb=0;rb<8;rb++) spi_data(fontdata[ra][rb]);
}
show_string(1,"Hello");
show_string(2,"World");
and that all works the characters are drawn in rows...