Digilent DIO2 User Manual

Page 11

Digilab DIO2 Reference Manual

Digilent, Inc.

www.digilentinc.com

page 11 of 19

VGA port

The five standard VGA signals Red (R), Green (G), Blue (B), Horizontal Sync (HS), and Vertical Sync
(VS) are routed directly from the B connector to the VGA connector, bypassing the CPLD. A resistor-
divider network is used to provide 8-bit color, with 3 bits for blue, 3 bits for green, and 2 bits for red
(the human eye is less sensitive to red, so red got 2 bits instead of 3). The resistor network uses the 75
ohm VGA cable termination to ensure that the color signals remain in the VGA-specified 0V – 0.7V
range. The HS and VS signals are TTL level, and come directly from the FPGA via the B connector.

VGA signal timings are specified, published, copyrighted and sold by the VESA organization
(www.vesa.org). The following VGA system and timing information is provided as an example of how
a VGA monitor might be driven in 640 by 480 mode. For more precise information, or for information
on higher VGA frequencies, refer to document available at the VESA website (or experiment!).

VGA systems and signal timings for a 60Hz, 640x480 display

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 permitivity through
the crystal on a pixel-by-pixel basis. Although the following description is limited to CRT displays,

DB15 VGA connector

Front view

Pin 1

Pin 6

Pin 11

Pin 5

Pin 10

Pin 15

Pin 1

Pin 15

DB15 through-hole pattern as

seen from the top

2
7

3
8

4
9

GND

DB15
Connector

To R0 on Connector B

Red

Green

Blue

Horizontal Sync

Vertical Sync

To R1 on Connector B

To G0 on Connector B

To G1 on Connector B

To G2 on Connector B

To B0 on Connector B

To B1 on Connector B

To B2 on Connector B

512

To HS on Connector B

To VS on Connector B