LCD


COMPUTRER_LCD.JPG

COMPUTER DISPLAYS
A computer display monitor, usually called simply a monitor, is a piece of electrical equipment which displays viewable images generated by a computer without producing a permanent record. The word "monitor" is used in other contexts; in particular in television broadcasting, where a television picture is displayed to a high standard. A computer display device is usually either a cathode ray tube or some form of flat panel such as a TFT LCD display. The monitor comprises the display device, circuitry to generate a picture from electronic signals sent by the computer, and an enclosure or case. Within the computer, either as an integral part or a plugged-in interface, there is circuitry to convert internal data to a format compatible with a monitor. vdu is also the most commonly used output device.



THE BASICS:
Liquid crystal display technology works by blocking light. Specifically, an LCD is made of two pieces of polarized glass (also called substrate) that contain a liquid crystal material between them. A backlight creates light that passes through the first substrate. At the same time, electrical currents cause the liquid crystal molecules to align to allow varying levels of light to pass through to the second substrate and create the colors and images that you see.

Active and Passive Matrix Displays
Most LCD displays use active matrix technology. A thin film transistor (TFT) arranges tiny transistors and capacitors in a matrix on the glass of the display. To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge until the next refresh cycle.
LCD.gif




LCDs vs. CRTs

If you are looking for a new display, you should consider the differences between CRT and LCD monitors. Choose the type of monitor that best serves your specific needs, the typical applications you use, and your budget.
Advantages of LCD Monitors
  • Require less power - Power consumption varies greatly with different technologies. CRT displays are somewhat power-hungry, at about 100 watts for a typical 19-inch display. The average is about 45 watts for a 19-inch LCD display. LCDs also produce less heat.
  • Smaller and weigh less - An LCD monitor is significantly thinner and lighter than a CRT monitor, typically weighing less than half as much. In addition, you can mount an LCD on an arm or a wall, which also takes up less desktop space.
  • More adjustable - LCD displays are much more adjustable than CRT displays. With LCDs, you can adjust the tilt, height, swivel, and orientation from horizontal to vertical mode. As noted previously, you can also mount them on the wall or on an arm.
  • Less eye strain - Because LCD displays turn each pixel off individually, they do not produce a flicker like CRT displays do. In addition, LCD displays do a better job of displaying text compared with CRT displays.
Advantages of CRT Monitors
  • Less expensive - Although LCD monitor prices have decreased, comparable CRT displays still cost less.
  • Better color representation - CRT displays have historically represented colors and different gradations of color more accurately than LCD displays. However, LCD displays are gaining ground in this area, especially with higher-end models that include color-calibration technology.
  • More responsive - Historically, CRT monitors have had fewer problems with ghosting and blurring because they redrew the screen image faster than LCD monitors. Again, LCD manufacturers are improving on this with displays that have faster response times than they did in the past.
  • Multiple resolutions - If you need to change your display's resolution for different applications, you are better off with a CRT monitor because LCD monitors don't handle multiple resolutions as well.
  • More rugged - Although they are bigger and heavier than LCD displays, CRT displays are also less fragile and harder to damage.
So now that you know about LCD and CRT monitors, let's talk about how you can use two monitors at once. They say, "Two heads are better than one." Maybe the same is true of monitors!



How the LCD works

The LCD doesn't do anything until you tell it to, it simply waits until it gets a valid enable rise and fall (which is when we put the enable pin high, wait for a while and then put the pin back low). At this point the display reads whether it is instructions or data to be processed, then whether it will receive or send information and last the data bits are sent or received.
In this article we will never receive information from the LCD so the R/W pin will always be low which means write.
The RS pin will be low except for when we print characters, everything else is considered instructions.
This makes it really simple to program the display.

When we know this we want to start with turning the display on and make it ready to receive information. This is done in the initialization sequence where we tell the display to be turned on, which "function set" to use, etc.
The power should already be on if you get the power from a spare power cable in the PC, otherwise this is the first thing to do.
Next is the "Function set" which is dependent on what display you have.
To make it more easy to understand I will explain exactly what we do when we use the function set.
DB2 is the Character Font bit and this should be low meaning 5x7 dot matrix.
DB3 is the Display Lines bit and should be high meaning 2 lines. What if you have 4 lines on the display? Don't worry, the first and third line are the same in the display memory so you should use high to.
DB4 is the Data Length bit and this decides if you have 4 or 8 DB, if you connect the display according to my schematics you should have this DB high.
Then set DB5 high to tell the display that this is indeed a "Function Set" instruction, then make sure that RS and R/W is low and do a enable rise and fall. For timings check the manual, i assume we only pause for microseconds when waiting for the display which should be much more than needed.


liquid crystal display device has a number of advantageous features including light weight, reduced thickness and low power consumption. LCD monitors have been widely applied to several portable information products, such as notebooks, PDAs, digital cameras, cell phones. The LCD monitors gradually replace the CRT monitors of the conventional desktop computers. Liquid crystal displays utilize such variations in optical properties to display an image. The LCD device is largely classified into a TN (twisted nematic) type and a STN (super-twisted nematic) type displays. Currently, the mainstream LCD is a TFT (thin film transistor) LCD, which is an active matrix type. Because of high displaying quality and small size, LCD monitors have become increasingly popular in a wide variety of applications.