Vga System Timing - Digilent Nexys4 DDR Reference Manual

Nexys4 DDR™ FPGA Board Reference Manual
9 VGA Port
The Nexys4 DDR board uses 14 FPGA signals to create a VGA port with 4 bits-per-color and the two standard sync
signals (HS – Horizontal Sync, and VS – Vertical Sync). The color signals use resistor-divider circuits that work in
conjunction with the 75-ohm termination resistance of the VGA display to create 16 signal levels each on the red,
green, and blue VGA signals. This circuit, shown in Figure 11, produces video color signals that proceed in equal
increments between 0V (fully off) and 0.7V (fully on). Using this circuit, 4096 different colors can be displayed, one
for each unique 12-bit pattern. A video controller circuit must be created in the FPGA to drive the sync and color
signals with the correct timing in order to produce a working display system.
Pin 1: Red
5 1
Pin 2: Grn
10 6 Pin 3: Blue
Pin 13: HS
15
11
Pin 14: VS
4KW
RED0
A3
2KW
RED1
B4
1KW
RED2
C5
510W
RED3
A4
4KW
GRN0
C6
2KW
GRN1
A5
1KW
GRN2
B6
510W
GRN3
A6
4KW
BLU0
B7
2KW
BLU1
C7
1KW
BLU2
D7
510W
BLU3
D8
100W
HSYNC
B11
100W
VSYNC
B12
Artix-7
Figure 11. Nexys4 DDR VGA interface.
9.1

VGA System Timing

VGA signal timings are specified, published, copyrighted, and sold by the VESA® organization (www.vesa.org). The
following VGA system timing information is provided as an example of how a VGA monitor might be driven in 640
by 480 mode.
NOTE: For more precise information, or for information on other VGA frequencies, refer to documentation
available at the VESA website.
CRT-based VGA displays use amplitude-modulated moving electron beams (or cathode rays) to display information
on a phosphor-coated screen. LCD displays use an array of switches that can impose a voltage across a small
amount of liquid crystal, thereby changing light permittivity through the crystal on a pixel-by-pixel basis. Although
the following description is limited to CRT displays, LCD displays have evolved to use the same signal timings as
CRT displays (so the "signals" discussion below pertains to both CRTs and LCDs). Color CRT displays use three
electron beams (one for red, one for blue, and one for green) to energize the phosphor that coats the inner side of
the display end of a cathode ray tube (see Figure 12).
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Other product and company names mentioned may be trademarks of their respective owners.
Pin 5: GND
Pin 6: Red GND
Pin 7: Grn GND
Pin 8: Blu GND
Pin 10: Sync GND
RED
GRN
BLU
HS
VS
HD-DB15
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