lcd display controller free sample

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The Hitachi HD44780 LCD controller is an alphanumeric dot matrix liquid crystal display (LCD) controller developed by Hitachi in the 1980s. The character set of the controller includes ASCII characters, Japanese Kana characters, and some symbols in two 28 character lines. Using an extension driver, the device can display up to 80 characters.

The Hitachi HD44780 LCD controller is limited to monochrome text displays and is often used in copiers, fax machines, laser printers, industrial test equipment, and networking equipment, such as routers and storage devices.

Compatible LCD screens are manufactured in several standard configurations. Common sizes are one row of eight characters (8×1), and 16×2, 20×2 and 20×4 formats. Larger custom sizes are made with 32, 40 and 80 characters and with 1, 2, 4 or 8 lines. The most commonly manufactured larger configuration is 40×4 characters, which requires two individually addressable HD44780 controllers with expansion chips as a single HD44780 chip can only address up to 80 characters.

Character LCDs may have a backlight, which may be LED, fluorescent, or electroluminescent. The nominal operating voltage for LED backlights is 5V at full brightness, with dimming at lower voltages dependent on the details such as LED color. Non-LED backlights often require higher voltages.

Character LCDs use a 16 contact interface, commonly using pins or card edge connections on 0.1 inch (2.54 mm) centers. Those without backlights may have only 14 pins, omitting the two pins powering the light. This interface was designed to be easily hooked up to the Intel MCS-51 XRAM interface, using only two address pins, which allowed displaying text on LCD using simple MOVX commands, offering cost effective option for adding text display to devices.

Vee: This is an analog input, typically connected to a potentiometer. The user must be able to control this voltage independent of all other adjustments, in order to optimise visibility of the display that varies i.a. with temperature, and, in some cases height above the sea level. With a wrong adjustment the display will seem to malfunction.

In 8-bit mode all transfers happen in one cycle of the enable pin (E) with all 8 bits on the data bus and the RS and R/W pins stable. In 4-bit mode, data are transferred as pairs of 4-bit "nibbles" on the upper data pins, D7–D4 with two enable pulses and the RS and RW pins stable. The four most significant bits (7–4) must be written first, followed by the four least significant bits (3–0). The high/low sequence must be completed each time or the controller will not properly receive further commands.

Selecting 4-bit or 8-bit mode requires careful selection of commands. There are two primary considerations. First, with D3–D0 unconnected, these lines will always appear low (binary 0000) to the HD44780. Second, the LCD may initially be in one of three states:

The same command is sent three times, Function Set with 8-bit interface D7–D4 = binary 0011, the lower four bits are don"t care, using single Enable pulses. If the controller is in 4-bit mode, the lower four bits are ignored so they can"t be sent until the interface is in a known size configuration.

In all three starting cases the bus interface is now in 8-bit mode, 1 line, 5×8 characters. If a different configuration 8-bit mode is desired, an 8-bit bus Function Set command should be sent to set the full parameters. If 4-bit mode is desired, binary 0010 should be sent on D7–D4 with a single enable pulse. Now the controller will be in 4-bit mode and a full 4-bit bus Function Set command sequence (two enables with command bits 7–4 and 3–0 on subsequent cycles) will complete the configuration of the Function Set register.

The execution times listed in this table are based on an oscillator frequency of 270 kHz. The data sheet indicates that for a resistor of 91 kΩ at VCC=5 V the oscillator can vary between 190 kHz and 350 kHz resulting in wait times of 52.6 µs and 28.6 µs instead of 37 µs. If a display with the recommended 91 kΩ resistor is powered from 3.3 volts the oscillator will run much slower. If the busy bit is not used and instructions are timed by the external circuitry, this should be taken into account.

The original HD44780 character generator ROM contains 208 characters in a 5×8 dot matrix, and 32 characters in a 5×10 dot matrix. More recent compatible chips are available with higher resolution, matched to displays with more pixels.

For the video display developer LCD panels are available in many sizes and resolutions, they are also available with many choices of maximum brightness. The following considers the topic of LCD panel brightness, the choices, the methods for adjusting brightness and some brightness adjustment scenarios.

LCD panels are generally rated as to their maximum brightness level which is expressed in Nits, it is equal to Candela/sqm (cd/m2), and this will be at a particular color temperature as noted in the specification, usually 10,000 K. In terms of a practical understanding, the following is a rough guide:

Outdoor displays range from a low end of 700 nits to typically 1,000 or 1,500nits and up with 2,000~2,500nits and even up to 5,000nits seen with some models. This may include standard LCD panels, custom LCD panels as well as custom cut LCD panels.

Virtually all LCD panels have a LED backlight these days, these are powered by an LED driver board. Brightness control via the driver board will be by one of two methods:

PWM (Pulse Width Modulation): This varies the duty cycle of the backlight “on time” – it is predominant in modern LCD panel LED backlight designs to enable support for digital brightness controls.

Backlight lifetime: Many LCD panels have a backlight lifetime rating of 50,000 hours (typically measured to half brightness), this can be extended by running the LED backlight at a lower brightness level. Some panels may only offer 30,000 hours as a lower cost solution while other panels may offer up to 100,000 hours for high end applications.

An LCD panel backlight may be constructed so the LED’s are mounted directly behind a light guide diffuser, or they may be mounted along one or more edges of the light guide.

Active backlight: This is a function of some LCD panel backlights to automatically adjust the backlight brightness in response to the image. For more advanced systems there is an LED array making up the LED backlight, this adjusts the brightness in areas localized to the image being shown. This can greatly enhance the brightness across the display and is being used primarily with video, for example on consumer TV sets. It is not useful to all image types, for example a spreadsheet or content like maps or data is not likely to benefit.

Local dimming: Some LCD panels with direct LED may support local dimming so the LED’s are dimmed in response to the image close to them. This will not be at the same resolution as the LCD panel itself but will help greater contrast over the display by enhancing the brightness in bright areas of the image and darkening the image in dark parts of the image.

For the LCD monitor manufacturer it is important to consider that any covering over the LCD panel will reduce the brightness. For example the protective glass over a digital signage display, or a touch screen, or a semi-silvered mirror. So if a specific brightness is required the measurement should be taken with these in place.

Examples of light meters costing a few hundred dollars include SpyderX by Datacolor (needs a PC), a handheld meter is the SM208 by Sanpometer (search SM208 meter). Note: Many light meters, including smartphone apps, will be meters used for photography and not give readings in nits (or candelas). LCD panel specifications are typically measured using nits.

PWM and Analog: Most Digital View LCD controllers support PWM and Analog as a method for adjusting the backlight brightness level (this is noted in the column headed “Other” on the controller board summary table: https://www.digitalview.com/controllers/lcd-controllers-home.html. Also see https://www.digitalview.com/blog/brightness-adjustment/ for a guide to using a dial or slider type variable resistor to adjust the backlight.

DPMS (Display Power Management System): The backlight will be automatically turned off after a period if there is no valid video signal being received.

Ambient light sensor: The backlight is adjusted for brightness or powered off depending on ambient light conditions. This uses a light sensor attached to the LCD controller board, see https://www.digitalview.com/blog/light-sensor-app-note/ for more details.

The specifics of the backlight control are documented separately for each LCD controller model (product summary here) in the product manual available for download on the product page.

Note: There are two ways to adjust the perceived brightness of a LCD panel or LCD monitor, the backlight and the black-level. Very often, particularly in the past, the monitor brightness setting adjusted the black-level, this adjusts the LCD but not the backlight.

Note: We have a blog on methods for implementing an ambient light sensor with Digital View LCD controller boards to automatically adjust the backlight or system power, see: Ambient Light Sensor

Update March 2019: Most of the above remains unchanged except for the increased availability of high bright LCD panels of around the 1,000 nit to 2,500 nit range. AUO for example has a number of large size LCD panels with 1,500 nit brightness for the digital signage market. Tianma has panels under 20″ with 1,000 nit to 1,500 nit brightness for various outdoor applications.

The other change is that high bright panels are now increasing edge-lit, this makes the panels thinner and these panels tend to use less power than the previous models. One of the benefits for monitor designers is easier heat management and reduced overall display system costs.