1. EEL 3705 / 3705L Digital Logic Design
Spring 2007 Instructor: Dr. Michael Frank Modules #90-99 (Extra Slides): Design Examples Module #91: VGA (Video Graphics Adapter) Color Video Driver Circuit
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

2. FLEX 10K: VGA Graphics Programming Examples
A Simple VGA Driver, Test Pattern Generator, and Character Generator for the FLEX 10K
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

3. Primary Colors in Kindergarten, vs. in Digital Video
Pigment color mixing
You may have been taught in kindergarten that red, yellow, and blue are the so-called “primary colors”…
and that all other colors can be produced by mixing these.
This is somewhat true, when it comes to mixing of absorptive pigments (paints);
red, yellow, and blue form a basis for the color space, such that many nice shades can be produced as weighted averages of them, by the mixing of pigments…
But, when it comes to light emission (e.g., from a monitor), the true primary colors are red, green, and blue.
This is because the eye’s three types of cones respond in the most discriminating way to light of these specific wavelengths…
any perceived color can be produced by adding together (not averaging) these colors in different amounts.
yellow
green
orange
blue
red
purple
Red light “on”
Blue light on
Green light on
Emissive color mixing
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

4. Retinal cone response curves & typical emissive RGB basis wavelengths
video green (~550 nm)
video blue (~450 nm)
video red (~700 nm)
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

5. M. Frank, EEL3705 Digital Logic, Fall 2006
A simple, generic variant of the old PC Video Graphics Adapter (VGA) standard
Colors: 8
3 bits, with 1 bit each for red, green, blue
000 = black, 001= blue, 010 = green, 011 = blue + green = cyan, 100 = red, 101= red + blue = magenta, 110 = red + green = yellow, 111 = red + green + blue = white
Display resolution:
640 pixels/row (horiz.) × 480 scan lines (vert.)
Display update frequency:
Usually ~30-60 Hz
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

6. M. Frank, EEL3705 Digital Logic, Fall 2006
VGA Cable Pinouts
(p.13)
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

7. M. Frank, EEL3705 Digital Logic, Fall 2006
Video Scan Line Timing
fclk = MHz; tclk = ns
782 tclk
(p. 26)
142 tclk
95 tclk
806 tclk
32.02 µs = 806 tclk
= 95 tclk
= 48 tclk
640 tclk = µs
= 24 tclk
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

8. Scan Line Timing Hardware
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

9. M. Frank, EEL3705 Digital Logic, Fall 2006
Video Frame Timing
trow = µs
514 rows
(p. 27)
34 rows
32 rows
11 rows
2 rows
525 rows
16.8 ms
15.37 ms
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

10. M. Frank, EEL3705 Digital Logic, Fall 2006
Frame Timing Hardware
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

11. Entire VGA Driver Schematic
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

12. Example Test Circuit for VGA Driver
Goal: Generate diagonal color test pattern
Computed by formula: RGB2..0 = (row + col)6..4
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

13. Photo of VGA CRT Monitor Screen
Circuit works perfectly!
Files are in VGA_example.zip on BB
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

14. Circuit to Demonstrate RGB Color Mixing
Project archive file:
VGA_RGB_demo_v2.zip
Under control of the first 3 DIP switches,
Display a solid red rectangle filling the right half of the screen;
display a solid green rectangle filling the bottom half of the screen;
display a solid blue rectangle filling the middle ¼ of the screen.
When multiple of these rectangles are turned “on” simultaneously,
in the regions where they overlap,
you can see the apparent colors that are produced by the various combinations of red, green, and blue light
Each filled rectangle is generated by appropriate comparators acting on the x and/or y screen coordinates
x ≥ 320
Is true on the right half of the screen
y ≥ 240
Is true on the bottom half of the screen
(160 ≤ x < 480) & (120 ≤ y < 360)
Is true in the middle ¼ of the screen.
Red rectangle
Green rectangle
Pushbutton inputs
Blue rectangle subcircuit
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006

15. Output of VGA_RGB_demo
Here is what the display looks like when DIP switches 1,2,3 are all “up”
9/19/2018
M. Frank, EEL3705 Digital Logic, Fall 2006