Chameleon-AVR Nurve Networks, Chameleon-AVR Datasheet - Page 52

• Manufacturer Part Number: Chameleon-AVR
• Description: MCU, MPU & DSP Development Tools AVR8 & PROPELLER DEV SYSTEM (SBC)
• Manufacturer: Nurve Networks

Specifications of Chameleon-AVR

• Processor To Be Evaluated: AVR 328P
• Data Bus Width: 8 bit
• Interface Type: USB, VGA, PS/2, I2C, ISP, SPI
• Operating Supply Voltage: 3.3 V, 5 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

phase difference from the color burst reference at the beginning of each line and the color burst tone of each pixel. In any
case, 8-10 clocks must be sent, I usually send 9-10 cycles of color burst. Each cycle at 3.579594 MHz takes 279.36 ns,
therefore, if you want 10 cycles of color burst, you must turn the color burst hardware on for 279.36 ns * 10 = 2.79 us
approximately.
“Back Porch” - Immediately following the color burst is the final part of the setup for the actual pixel data, this is called
the “back porch” and should last 1.6 us.
11.2.6 Generating B/W Video Data
The remainder of the video information is 52.6 us, this is where you insert your pixel data. Now, if you wanted a B/W only
signal then you would modulate the video signal from BLACK (0.3V) to WHITE (1.0V) for the remainder of the line and be
done with it. For example, each line could rasterize a line buffer, or a sprite and different values would map to different
voltages from BLACK to WHITE. With this approach most TVs have an input bandwidth wide enough to display about 320
luminance changes per active line, that means that no matter how fast you try to change the luminance signal only 320
times a line will you see anything. Let’s see how we roughly estimate this.
The line length is 52.6 us, we want to make 320 changes in that time, that means that we need to send data at a rate of:
Inverting this gives us the frequency which is 1/164.375 ns = 6.0 MHz roughly! Ouch, that means that the input to the TV’s
luminance has to be 6.0 MHz or greater. Sorry to say, it’s not. In most cases, you are lucky if you get 4.5 – 5.0 MHz input
bandwidth, this 320 is a definitely upper limit on B/W luminance transitions per line.
11.2.7 Generating Color Video Data
Generating color video is much more complicated than B/W, however, if we take a practical approach rather that a
mathematical, its quite easy. Forgoing the complex quadrature encoding of color and luminance and the encoding and
decoding of the signals, creating a color is very easy. For each color clock on the active scan line, you must generate a
3.579594 MHz sine wave, this must ride on top or be superimposed on the luminance signal (the Chameleon AVR
hardware does all this). The overall amplitude of the signal is the brightness or luminance just as it was with B/W, but the
color signal’s saturation is simple the peak-peak (p-p) value of the color signal 3.579595 MHz signal as shown in Figure
7.6. The actual color that is displayed has nothing to do with the amplitude of the video signal, but only the PHASE
difference from the reference burst from the original color burst reference at the beginning of each line.
To re-iterate, to generate color, we simply produce a 3.579594 MHz signal, superimpose or add it to the overall luminance
signal, and the phase difference between our color signal and the reference is the color on the screen! Cool.
Taking this further, let’s break up the line into pixels once again and see how many can be displayed each line. There are
52.6 us of active video time. We have to generate a 3.589594 MHz signal and stuff it into each pixel; given this how many
pixels can fit into a line?
Calculation of Color Clocks Per Line
This means that at best case you can have 188 colored pixels per active scanline, but it gets worst! That doesn’t
necessarily mean that you can have 188 DIFFERENT colored pixels across the screen, it just means you can request that
from the poor TV with limited bandwidth. Again, this is a give take world, and in many cases, you would never have 188
different colors on the same line, it would look like a rainbow. In most cases, objects have constant color for a few pixels
at a time. In any case, many video system over drive the video to 224, 240, or 256 virtual pixels (but, the color will not
change that fast), you can do this if you wish, however, I suggest using a nice 160 x 192 display or thereabouts which will
always look pretty good, has enough resolution, and you will almost get a 1:1 color change per pixel even if you change
each pixel’s color. However, give everything a try and see what you get.
52.6 us / 320 = 164.375 ns per change
52.6 µs / (3.579594 MHz
-1
) = 188.
© 2009 NURVE NETWORKS LLC “Exploring the Chameleon AVR 8-Bit”
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