FEATURE DISPLAYS & UIS
INTELLIGENT DISPLAY MODULES AND HOW THEY CAN HELP EASE YOUR DESIGN
Incorporating an LCD into your design – should you make a discrete design or use a COTS display module? Markku Riihonen, products development manager at 4D Systems offers some answers
T
here are very few embedded designs on the market today that don’t have
a display. There is no doubt that the smartphone has accelerated the trend of incorporating touch displays into virtually every electronic device we use in our daily lives. A well-presented, visually pleasing and intuitive display is also seen to strengthen product brand value and user confidence. There are practical reasons too for using a touch-enabled LCD. It removes the need for a myriad of push buttons that not only add cost, but also collect dust and potentially allow ingress of moisture and particles inside the product enclosure. Using a capacitive touch screen, for
example, allows the designer to keep a tight seal between the glass display and the enclosure and allows any number of buttons, wheels and slider controls to be used as required by the application. Whether you decide to use an off-the-
shelf display module or embark on a discrete design, there are a number of decisions to be made that are common to both approaches and shape the core part of the application’s design. Firstly, what size does the display need to be? Will it fit into the space envelope of the product? For battery powered products there is the further complication of power consumption. Determining likely battery life for a number of use cases is a key factor not only from the design aspect, but it can also have a significant impact on the product’s success. When it comes to adding a display
there are basically two choices: design a discrete display from scratch or use an off-the-shelf module. Let’s look at the discrete approach first. In an embedded system using a TFT
LCD, the MCU is tasked with composing the image to be displayed in the frame buffer. The buffer is essentially volatile memory that is used to store each pixel to be displayed. The display size directly dictates the size of the frame buffer memory, and typically provision is made for one buffer. In composing the image the MCU needs to be able to incorporate images and icons in addition to processing the data to be displayed. The display (video) controller constantly reads the frame buffer and writes it to
12 NOVEMBER 2017 | ELECTRONICS Initially the attraction of implementing
a discrete design may be driven by keeping the bill of materials (BOM) cost as low as possible, but this needs to be balanced against the time, and therefore the additional cost, to design it. The alternative approach is to use an
Figure 1:
Use of TFT LCDs in a retail application (source Stiegl Getränke & Service GmbH & CO. KG)
the display glass, typically at a rate of 60Hz. Typically screens below 4.3 inches in size include a display controller IC. Displays greater than 4.3” will exclude the controller, so this needs to be added into the design. Separate display controllers usually
have frame buffer memory on the die. Clearly the MCU needs to be capable of running the display and frame buffer tasks in addition to the core application. Drivers are needed for the display
Figure 2:
4D Systems 4.3-inch gen4-uLCD-43DCT-CLB module (source 4D Systems)
controller, and primitives need to be written to allow icons, fonts and stored images to be written to the display. Such primitives also need to include basic graphic functions such as drawing lines, circles and boxes, and that’s before you can consider establishing any form of GUI for the application. The display hardware needs to laid out around the main application and everything debugged and tested before you can get anywhere near developing the GUI. It’s highly likely the above might take a seasoned embedded developer 4–6 months to achieve.
intelligent display module. Such a module usually features an industry standard interface for communications to the host in addition to its own MCU. Using the module approach has the benefit that all of the drivers, primitives and GUI functions have already been developed and tested. Also, the host MCU can offload all the display tasks to the module so that the host can dedicate all its resources to the application. An example of a suitable module is the
4.3-inch gen4-uLCD-43DCT-CLB from 4D Systems (figure 2). Featuring a capacitive touch controller, it is powered by a 4D Systems Diablo16 Graphics Processor and offers a comprehensive range of peripheral interfaces including 16 configurable GPIOs, some of which can be used for PWM, I2
C, SPI, Quadrature
input and an ADC input. It also is equipped with a microSD card slot that provides a local FAT16 storage capability for graphic images and storing data. The module can be used in a number of
different ways to suit the host application. In fact, if the application does not warrant a lot of resources or complexity, the main application code could be run on the module as an intrinsic part of the graphic processing code. Normally that would not be the case, and the module will interface with the host. When faced with adding a graphical
LCD display to a design, it is important to carefully consider whether a discrete approach could be accommodated within the project timescales and cost budget. Intelligent display modules, together with their graphical design tools, can significantly speed the whole design process, ensuring that working prototypes can be delivered in the shortest time possible.
4D Systems
www.4dsystems.com.au T: +43 660 753 0499
/ ELECTRONICS
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