Datasheet

Pmod VGA Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 2 of 5
Pin
Signal
Description
1
B0
Blue 0
2
B1
Blue 1
3
B2
Blue 2
4
B3
Blue 3
5
GND
Power Supply Ground
6
VCC3V3
Positive Supply Ground
7
HS
Horizontal Sync
8
VS
Vertical Sync
9
NC
Not Connected
10
NC
Not Connected
11
GND
Power Supply Ground
12
VCC3V3
Positive Power Supply
Table 1. Pmod header J2.
1.1 Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 1.7 inches (4.3 cm) long on the sides parallel to the
pins on the pin header and 1.7 inches (4.3 cm) long on the sides perpendicular to the pin header.
2 Functional Description
The Pmod VGA uses 14 input pins to create an analog VGA output port. This translates to 12-bit color depth and
two standard sync signals: Horizontal Sync (HS) and Vertical Sync (VS). The digital-to-analog conversion is done
using a simple R-2R resistor ladder. The ladder works in conjunction with the 75-ohm termination resistance of the
VGA display to create 16 analog signal levels for the red, blue, and green VGA signals. This circuit produces video
color signals that proceed in equal increments between 0V (fully off) and 0.7V (fully on). With 4 bits each for red,
blue, and green, 4096 (16x16x16) different colors can be displayed, one for each unique 12-bit pattern.
When used with an FPGA host board, a video controller circuit must be created in programmable logic to drive the
sync and color signals with the correct timing in order to produce a working display system. It may be possible to
drive the video signals using a very fast microcontroller with a parallel bus controller; however, Digilent does not
provide examples for this use case.
2.1 Interfacing with the Pmod
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).