Design Recipes for FPGAs
164
This process returns the current value of the pixel data into a sig-
nal called pixel_data which is declared at the architecture level:
signal pixel_data : std_logic_vector ( 7 downto 0 );
This has the red, green and blue data defined in lowest 6 bits of
the 8 bit data word with the indexes, respectively, of 0–1, 2–3, 4–5.
Horizontal sync
The next key process is the timing of the horizontal and vertical
sync pulses, and the blanking intervals. The line timing for VGA is
31 770 ns per line with a window for displaying the data of 25 170 ns.
If the FPGA is running at 100 MHz (period of 10 ns) then this
means that each line requires ...