New-Tech Europe Magazine | August 2017

Crystal clear choice for displays

Mary Tamar Tan, Applications Engineer at Microchip Technology, Rodger Richey, Director Engineering and New Product Development at Microchip Technology

Microcontrollers with integrated drivers are providing a boost for the growing LCD market Liquid crystal displays (LCDs) have soared in popularity in recent years thanks to numerous advantages over other display technologies. Controlling them has also become easier because of the introduction of 8bit microcontrollers with integrated LCD drivers. Prominent features of such LCD controllers include contrast control, drive waveforms, biasing methods and power modes. These devices can directly drive segmented displays with letters, numbers, characters and icons and have been developed to meet low-cost design requirements. A good example are the PIC microcontrollers from Microchip, which are available in 28-,

40-, 64-, 80- and 100-pin packages and can eliminate the need for several external hardware components. The LCD driver module generates the timing control to drive a static or multiplexed LCD panel with support for up to 64 segments multiplexed with up to four or eight commons. Fig. 1 shows a typical LCD module block diagram. The number of LCD registers varies depending on the maximum number of commons and segments that can be driven by the specific device. Timing control block As shown in Fig. 1, the timing control block comprises the LCD control register (LCDCON), LCD phase register (LCDPS) and LCD segment enable registers (LCDSEx). The LCDCON controls the overall

operation of the module. Once the module is configured, the LCDEn bit is used to enable or disable the LCD module. The LCD panel can also operate during sleep mode by clearing the SLPEn bit. The bits determine the LCD clock source and the configuration must comply with the LCD glass driving scheme. The LCDPS configures the LCD clock source prescaler and the type of waveform. The prescaler select bits have a direct effect on the LCD frame frequency, so must be set accordingly to avoid ghosting or flickering on the display. The LCDSEx configure the functions of the port pins. Setting the segment enable bit for a particular segment configures that pin as an LCD driver. Likewise, clearing the segment enable bit allows the pin to function as an IO port.

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