The use of icons and graphical menus is now accepted as the preferred method for implementing a user interface, be they image overlays for mechanical switches or ‘soft’ buttons on a touch-sensitive graphical display.
Simply put, a graphical user interface can make products more approachable and engaging for the user, and help add value and differentiation for the OEM.
The use of images to replace or supplement text makes sense for many reasons, not least because it can break down language barriers or remove the need for specialist knowledge. Users now expect progressive graphical interfaces that improve a product’s look, feel and use; an expectation which OEMs are eager to meet. This is driving demand for simple but capable graphics solutions that are both technically suitable and commercially viable.
To this end, Microchip has developed a family of PIC microcontrollers that provide a fully integrated and competitive solution to implement a graphical user interface, with the support needed to deliver a total system solution.
Market development
The consumer, industrial and automotive markets are all experiencing greater demand for displays and growth of this kind in the electronics industry typically results in aggressive price erosion. The net effect is rapid technological advancement, which enables a second wave of adoption in applications where the price of the technology would have previously been prohibitive. While this is effectively opening new markets for existing display technology, the opportunity can only be grasped if the total system solution still meets the commercial parameters of the target market.
In the case of LCD technology, the display is not the only consideration; driving a display can require a more powerful processor and additional components such as a graphical display controller or additional memory. Along with the additional hardware requirements, the software complexity rises significantly in relation to the sophistication of the display and graphical elements. This complexity can easily become a dominant component in the development process, as it often requires disparate skills which may also need additional engineering effort. These elements can add cost to a system and complexity to the design, both aspects that increase the risk and time to market for new developments.
This has created a need for effective solutions for implementing graphical user interfaces; however, integrated solutions that target display technology are often developed for high volume and high margin markets, such as industrial control and automotive, which creates a technology vacuum for OEMs who need to implement sophisticated graphical user interfaces without increasing system cost and complexity.
The solution, until now, has either been to adopt a more expensive application-specific device or add additional integrated circuits to create a graphical display sub-system – both of which present significant commercial and technological challenges. With the introduction of the PIC24FJ256DAXXX and associated design tools, Microchip has removed those challenges by delivering a fully integrated, advanced graphical solution that is both easy to use and appropriate for cost sensitive applications.
Overcoming challenges
The challenge associated with display technology is partly technical – developing the graphical interaction, driving the display and correlating that to the system’s control functions are additional design elements for applications that do not already employ a graphical user interface. But there is also the commercial challenge associated with this, in terms of meeting the technical requirements in the most cost efficient way. The PIC24FJ256DAXXX family has been developed to address all of these challenges, by integrating new features never before seen on a PIC MCU, but which also benefit from Microchip’s experience and established development tools for GUI design.
The PIC24FJ256DAXXX uses the same modified Harvard architecture CPU as other PIC24F family members. However, the new family integrates three dedicated graphic acceleration engines and a display controller. These engines support a DMA interface to the frame buffer memory, effectively driving graphics performance in processing and rendering graphics objects, providing easy switching between fonts and languages, and fast data or image decompression. The on-chip display controller is capable of directly driving almost any LCD/LED display with an RGB or STN/CSTN interface, which includes a wide range of TFT LCDs and some OLED displays. These features effectively create a complete graphical sub-system fully integrated on the same chip as the MCU, driving a 640 by 480 display (VGA) at 16 bpp/30 Hz or 8 bpp/60 Hz, or a 480 by 272 (WQVGA) at 16 bpp/60 Hz.
Additionally, the PIC24FJ256DAXXX is available in two memory configurations which can be used for frame buffering: 24 KB or 96 KB of RAM. Depending on the display size, resolution and colour configuration, this integrated memory delivers cost savings when supporting monochrome, greyscale or colour displays up to 320 by 240 with 256 different colours (8 bpp) without external RAM, thereby increasing the screen resolution and colour depth. Table 1 shows the possible configurations for a given screen resolution, with or without an external frame buffer.
The frame buffer is used in conjunction with an on-chip colour lookup table. This allows a palette of 256 non-continuous colours chosen from the full 16 bpp RGB range of 64 000 possible colours, giving a truly rich user experience without increasing system resources. Each frame can use a different palette of 256 colours, enabling a huge variety in graphical capabilities that can be applied to, for example, multiple menus or operation modes. Figure 1 demonstrates some of the results that can be achieved through the use of different colour palettes.
All of these integrated features address the commercial issue of minimising cost and number of components – by integrating all of the additional hardware necessary to drive an LCD/LED display, the PIC24FJ256DAXXX family lowers the bill-of-materials cost and system cost compared to configuring a graphics sub-system using discrete display controller and RAM, or more expensive displays with an integrated controller and/or frame buffer.
The new PIC family is supported by Microchip’s Graphical Display Designer and Graphical Library software suite, which are free to Microchip customers. The Graphics Display Designer is a visual design tool, using GUI ‘wizards’ to help with graphically designing screen layouts and elements. The tool works in conjunction with Microchip’s graphics library, a repository of pre-configured graphic elements including fonts, objects and graphic primitives.
Using Graphics Display Designer, engineers can configure a user interface without the need to write any code – the tool does all the hard work. If greater control over the design is needed, elements in the graphics library can still be referenced using the API, however the approach offered by the Graphics Display Designer accelerates the early stages of development and can, in many cases, reduce or remove the need to manually write code to drive or interface to the screen.
Total control solution
Many low-cost MCUs today can implement a simple graphical user interface but with the PIC24FJ256DAXXX those same applications can offer more sophisticated user experiences without increasing system cost. System architects can develop a solution capable of driving a display of various resolutions using a selection of 256 colours chosen from a total of 64 000 different RGB colours, at refresh rates of up to 60 Hz.
Furthermore, the PIC24FJ256DA210 provides extensive support for capacitive sensing and resistive touch screens, through its mTouch interface and analog-to-digital converter (ADC) respectively. Microchip’s mTouch technology enables robust capacitive touch-sensitive controls on front panels, while LCD/LED displays with built-in resistive touch technology can be easily interfaced to the PIC24FJ256DA210.
As with other PIC24F families, the PIC24FJ256DAXXX family also offers comprehensive wired communication peripherals including USB OTG host/slave and mini-host support, four UART modules, three I2C modules and three SPI interfaces. The four low-power modes of the PIC24FJ256DAXXX family support a lowest typical supply current of just 20 µA, which can be used to wake up the system and turn on the display with touch button response.
Developers can start exploring the advanced features of the PIC24FJ256DA210 through a dedicated development platform, available with either a 3,2” or 4,3” colour TFT display. The new PIC24F devices are also supported by the existing free graphical software suite, webinars and training notes.
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