April 21, 1998
Two Graphic Liquid Crystal Controller/Drivers, Providing Single-Chip Implementation of Graphic Display and Character Display for Mobile Communication Products- Switchable between 96 x 42-dot Graphic Display and 5-Line x 16-digit Character Display in a single chip -These new products enhance Hitachi's lineup of graphic liquid crystal controller/driver series with the ability to provide a simple character display with the flexibility of a graphic display. The graphic liquid crystal controller/drivers will enable more sophisticated information services to be offered, while built-in key-scan functions will make it possible to create systems that are smaller, lighter, and lower- priced. These two products will be available in chip- with-bump*3 or TCP*4 mountings. With the rapid growth of the market for mobile communication products such as portable and PHS phones, there are constant demands for lower power consumption, greater multifunctionality, reduced size and weight, and lower costs. With the increasing multifunctionality and higher added value of the small LCD displays used in these products, it has become necessary to provide not only a character display, based on kana and alphanumeric characters, but also a graphic display to implement such additional functions as kanji message communication, games, and schedulers. With existing graphic display systems, however, the character display is laborious and imposes a heavy software processing load on the microcomputer, leading to correspondingly long system development times. In response to this problem, Hitachi has developed the new concept graphic liquid crystal controller/driver series capable of switching between graphic display and character display according to the display requirements of the system. The HD66724, switchable between a 72 x 26-dot graphic display and a 3-Line x 12-digit character display, was already in volume production as the industry's first graphic liquid crystal controller/driver. The controller/drivers of new products have an on-chip low-power-consumption type liquid crystal drive power supply circuit, and include circuits for 4 x 8 key matrix control and control of three LEDs or back lights. Also included is a synchronous serial interface for interfacing to a microcomputer, and 68/80-type 8-bit and 4-bit interface functions. Access to on-chip registers and RAM can be performed by continuous high-speed writing, independently of the internal operating clock frequency, enabling fast data transfer to be achieved. In addition, the built-in key-scan and port control functions make it possible to control the entire operating display, including the liquid crystal display and key matrix, via three serial interfaces. This makes it possible to use fewer parts and to cut the number of microcomputer I/O ports by more than 20, for example, resulting in lower system size, weight, power consumption, and costs. Regarding display function, in graphic display the display data is written directly to the 96 x 42-dot (HD 66726) or 96 x 26-dot (HD66725) bit-mapped display RAM. Kanji message display, games, etc., can be supported by writing a kanji font or patterns to the display RAM. In character display, the display automatically generates character font pattern from 8-bit kanji. There are 432 fixed and 64 user-programmable 6 x 8-dot fonts, enabling a wide variety of characters to be displayed, including characters in boldface fonts and numerous national fonts. In addition, blink control can be performed for displaying marks such as pictograms and icons. To achieve a further reduction in power consumption, the internal operating clock frequency has been lowered to 32 kHz from the previous 120 kHz, and event-driven operation, in which unnecessary operating clocks are stopped on an individual function block basis, is employed in the driver unit. A newly supported feature is a partial display-on function that reduces power consumption to approximately 50% compared to previous Hitachi products, by minimizing the liquid crystal drive duty and drive bias, and the liquid crystal drive voltage, when displaying a "standby" or similar mark, or during time and similar displays which use only part of the display screen. Combined use of the internal oscillation clock stop function (standby function) and the liquid crystal drive power supply-off function provides power management that is finely tuned to synchronize the operation. This power management system enables new products a drastic reduction in the total power consumption of the liquid crystal display system, including the liquid crystal drive power supply system. The power consumption figure is approximately 210 microwatt (HD66726) or 150 microwatt (HD 66725) during full-screen display and approximately 60 microwatt during pictogram display in standby mode, and approximately 3 microwatt with no display (stand by mode). Supported mounting methods are COG*5 mounting, in which the device is directly mounted face-down on the LCD glass, COF*6 mounting, in which the device is mounted face-down on a flexible film substrate, and TCP mounting, in which the device is connected to the LCD glass via a heat seal. To minimize the mounting glass area in COG mounting, a slim chip shape is used, with a width of only 2.51 mm. In addition, the HD 66726 supports COB*7 mounting. Hitachi plans to expand the product lineup in the future, based on the present technology, to provide support for larger display sizes.
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