Alpha-numeric modules display characters, numerals, symbols and some limited graphics. Interface is achieved via a bi-directional, parallel ASCII data bus. Necessary features such as Character Generation, Display RAM Addressing, Cursor Scrolling, Blanking, and Handshake are all included. User programmable fonts are supported. In summary, these modules are the simplest and most economic means to communicate meaningfully between any micro-system and the outside world. Their inclusion adds to any product's appeal.

Alpha-numeric modules range from 8 to 80 characters per line. One, two or four character lines may be chosen. Character height spans 0.130" (3.31 mm) to 0.500" (12.71 mm). Most formats are available in a variety of packages to meet various mounting requirements. Multi-line models offer the best value when analyzed by a "cost per character" basis. Displays are readable both day and night by selecting a backlight option. Extended temperature modules are available which operate between -20 and +70C.

For requirements of more than 4 lines or 40 characters across, select a graphic formatted module. Graphic modules are also used when different sized characters are needed, and when special fonts such as Chinese or Arabic are required.

Selecting the exact version of an LCD once the format is decided is largely a subjective judgement. Color, fluid type, and backlighting determine the overall look of the display and often the appearance of the end product. Operating conditions such as temperature, lighting conditions, and available power are also factors in determining the type of display to use.

The following sections explains the optical characteristic options available in A/N modules,

B. FLUID TYPES

TN Fluid

TN Fluid is the least expensive type. The viewing angle is about 40-45, and must be designated "top" or "bottom" view preference. Bottom view is used when the user will be below the plane perpendicular to the display, such as on a desk calculator. Top view is used when the display is mounted on a vertical surface below eye level. See diagram below.

TN Viewing Cone

STN AND NTN Fluid

STN and NTN are both high contrast and wide viewing angle fluids. They differ in the level of contrast and viewing angle they achieve. Both can be seen above and below the plane perpendicular to the display. See the diagram below.

NTN and STN Viewing Cone

The vertical viewing cone on all fluids can be adjusted by controlling the VO voltage. The range of adjustment is shown in the viewing angle charts below. The horizontal cone is relatively fixed.

C. VIEWING MODES

The fluid type, polarizers and module construction determine the viewing mode and colour of the display. Displays are either "postive image", dark characters on a light background; or "negative image", light characters on a dark background. Backlight capability is determined by the presence or absence of a reflector or transflecter on the back side of the glass.

Reflective displays have a full reflector. The cannot be backlit. They offer the lowest power option and the best contrast in high ambient light conditions. They are not available in "positive image".

Transmissive displays are usually negative image and are backlit for best readability. They can be used in well lit indoor conditions to dark environments, typically not recommeded for daylight usage. They offer a different appearance than typical LCDs, bringing a light emitting look to the product.

Transflective displays combine the features of reflective and transmissive modes. These positive image displays can be read in all lighting conditions. The backlight can be turned on for low light levels or operated continuously to add the light-emitting look to a product.

Positive Image	Negative Image

Colors

TN positive image displays will have a silver/grey background and dark, almost black characters. In the negative image, the background will be black and the characters will be the color of the backlight, usually yellow/green or white. (See section on backlighting).

NTN and STN positive image displays can have a silver or yellow background with dark characters. Negative image versions have a dark blue background, characters are the folour of the backlight.

Choice of color is determined by what fits best in the package. Not all NTN displays are available in all colors. Consult us for current availability.

D. BACKLIGHTING CHARACTER MODULES

1) EL Backlighting

EL backlighting is the original LCD backlight. It is thin, lightweight, low power, and fits between the glass assembly and PCB without any modification to the module. Most positive mode displays are furnished with a blue green lamp. Negative mode displays usually come with a white lamp. Other colors can be specially ordered.