VGA LCD FAQ Revision 1.0
By Randy Schafer
© 1999 Earth Computer Technologies
This document may be distributed freely only in its entirety.
http://www.earthlcd.com
Purpose of this FAQ? This FAQ is designed to discuss what is a VGA LCD and how does it interface and how is it used in an application.
Who is Earth Computer Technologies? We are the world’s largest remarketer of VGA LCD’s. We buy and sell surplus LCD inventory worldwide. We also build controllers, touchscreens and monitors to help sell these surplus LCD’s.
Why we did this FAQ? To educate technical personnel on what is a VGA LCD and how to use them in various applications.
Why did we call this a VGA LCD FAQ? This is what people seem to call graphical LCD’s of VGA or higher resolution. It also generally describes the type of LCD used in a notebook computer. Some of this may apply to smaller graphical LCD’s with one exception. The exception is some smaller graphical LCD’s have on board controllers while as of this writing VGA LCD’s do not have on board controllers.
Can I plug a VGA LCD into my PC? No not directly without some type of controller card.
Can a VGA LCD be used as a VGA monitor on my PC? Not without a controller of some type. With an analog LCD controller like the EarthVision/ADC you could drive an LCD from an existing VGA card. This analog controller has a DB-15 VGA input like a standard PC monitor. You could also use a special VGA card that has digital outputs designed to drive a LCD like the EarthVision/PCI.
What is a VGA LCD? A VGA as discussed in this document is a 640 x 480 resolution LCD. This material could apply just as well to SVGA (800 x 600 pixels), or XGA LCD. A VGA LCD does not have a controller built in at all. Because they are called a VGA LCD does not mean it can hook to a P.C. VGA port (ie. The DB-15 port on the back of your P.C.) A VGA LCD is a digital LCD that has drivers on it that address pixels by row and columns. These drivers are driven by digital signals that consists of a pixel clock, horizontal and vertical timing signals and data bits. There is no memory in the LCD and the pixels are sequentially accessed. The LCD must be constantly supplied timing and data information at a specified rate usually form 60 to 150 frames of data per second. Improper signal timing can actually damage an LCD.
Can I run a VGA LCD off a microcontroller like a PIC directly? No. The bandwith just for a 256 color STN display is 13 megabytes per second and the address space is 307k bytes. If you used an LCD controller chip interfaced to a PIC you could run it but it would have very slow screen updates. We will introduce an RS-232 intelligent LCD controller in the 3rd quarter that will allow you to do run easily off microcontrollers.
What is required from Earth Computer to run a VGA LCD? A controller and a cable and an inverter (if the display is a backlite type). These are available in kit form.
Are all LCD’s compatible? Life should be so simple! Different models use different interface connectors, timing (set by the controller card BIOS), different mounting dimensions and backlight inverter requirements.
TO BE CONTINUED ……
TYPES
STN
DSTN
TFT ACTIVE COLOR
TRANSMISSIVE
REFLECTIVE
TRANSFLECTIVE
INTERFACE
VGA LCD CONTROLLERS
BRIGTNESS
RESPONSE TIME
CONTRAST RATIO
TERMS
Analog VGA