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This means that they don’t have to be drawn and redrawn anew, they are simply accessed from a display list. As a result rather than having to render the display pixel by pixel, they can be rendered line by line at 1/16th of a pixel resolution, with the upshot that there are substantial savings in the required bandwidth. As this object-oriented approach to HMI design leads to a marked reduction in the data transfer involved, the frame buffer and the large non-volatile memory can be eliminated from the design. The EVE chip’s internal object memory is more than sufficient for storing/executing several thousand different objects and rendering the display through its own built-in buffer. Since the EVE chip can take care of the majority of the graphics processing, the microcontroller does not need to allocate much of its functionality to this task. As a result an 8-bit microcontroller will be more than adequate for the HMI system. Low bandwidth SPI or I2C serial interfaces can be used for data transfer, as opposed to the wide parallel buses shown in Figure 1. For objects with a higher degree of complexity (such as keys, sliders, toggles, buttons, gauges, clocks, etc.) special EVE widgets have been designed. This means that rather than having to create them for scratch, all the engineer has to do is adjust the size colour and location that suits their particular HMI design. Touch tagging allows any coordinates within a certain area (e.g. coordinates delineating a button), rather than a specific point, to activate an assigned touch operation. This thereby reduces the risk of an incorrect touch response occurring, while also keeping the data transferred between the display and the supporting electronics to a minimum. Other advantages of migrating to an object-oriented methodology include its more effective way of dealing with animated content. Whereas a conventional HMI system would have to keep redrawing what was going to be shown on the display again and again so as to accommodate the changes that occur during the animation, for this more innovative approach all that is needed is to update the coordinates that an object is to be placed at. A single object can also be repeated in multiple locations. This avoids having to waste bandwidth creating new objects many times. Finally, the anti-aliasing function enhances the quality of the images rendered, removing the jagged edges on lines and complex shapes. Application example The methodology just detailed proves much more effective for systems in which a number of HMIs are being interfaced together. Figure 3 describes a set up where data transfer is taking place between a pair of HMI sub-systems which have been connected to one another via an RS232 interface (though it could of course be applied equally well to other interface technologies such as Ethernet). The respective HMI sub-systems are both reliant on a VM800P ‘Plus Board’ EVE evaluation module, with an attached VI800A-232U module. Each VM800P consists of an Atmel ATMEGA328P microcontroller, an FT800 EVE device from FTDI Chip, a 4.3-inch touch-enabled display, an SD card connector (for accessing stored data on an SD card) and a real-time clock (RTC) with battery backup. Application firmware The firmware included in the example code allows the transferring data from one VM800P to the other through the VI800A- 232U daughter cards attached to each. In this particular case the data consists of a series of images, which are designed to demonstrate the capacity for data to be transferred both physically and visually. mouser.com/new www.electronics-eetimes.com Electronic Engineering Times Europe June 2015 31 Future products_93x277_UK.indd 1 18/05/15 10:33


EETE JUN 2015
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