Programmable circuit for controlling a liquid crystal display

Details Programmable circuit for controlling a liquid crystal display Programmable circuit for controlling a liquid crystal display

1986-11-06

1989-06-13

Yusko, Donald J.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340799, 340750, G09G 336, G06F 3147

Patent

active

048396389

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a control circuit for controlling a liquid crystal display (LCD controller) for two separate bus structures of which one serves for the exchange of data with a computer while the other serves for the exchange of data with at least one addressable memory associated with the liquid crystal display (LCD).
Circuits of this type are known, which make it possible to derive the information-containing signals required to control a liquid crystal display (LCD) module organized in the form of a matrix from a processor system, with the clock pulse and timing control signals for the LCD being generated in the control circuit itself. Most of the characters to be displayed are generated with the aid of memories provided in the control circuit itself which are able, upon an appropriate instruction, to display complete characters on the LCD.
In customary liquid crystal displays with high resolution signal sequences must be produced--corresponding to the matrix-type actuation--which, on the one hand, emit a sequential succession of signal patterns corresponding to image lines and, on the other hand, take care that the characters are newly recorded, for example with the use of the known "two thirds methods", in regular repetition and, additionally, polarity reversals are effected at certain intervals to avoid electrolysis phenomena in the liquid crystal arrangements. Moreover, switching means should be provided, if required, to supply a plurality of the display faces in parallel since the maximum area to be actuated is limited by the repetition intervals to be maintained. The thus generated signals reach the LCD module by way of driver stages.
The drawback is that the prior art control devices for changing the image contents require more or less complicated operations which all have in common that access by the processor to the memory region associated with the LCD is possible only indirectly, after a corresponding request by way of the control circuit, with waiting cycles and similar delays having to be accepted. In other embodiments, the contents of the liquid crystal display can be displayed only indirectly via a memory which itself contains the components required to generate complete characters composed of groups of dots.


SUMMARY OF THE INVENTION

In contrast thereto, it is an object of the invention to substantially simplify a control device of the above-mentioned type, with changes in the contents of the image on the screen taking place as independently as possible from the function cycles of the control circuit without consideration of special time conditions.
The invention is based on the realization that optimum processing, with respect to time, of signals contained in a display memory is possible if the memory region associated with the display is essentially independent of the internal control sequence of the circuit and substantially uninfluenced by the times required to supply the screen with data from the memory. The access times for actuating the LCD module can then always be kept so short that data access from the computer system is not or hardly impaired with respect to time.
The control circuit is thus "quasi transparent" for the connected computer so that a change in the screen (memory) contents can always take place without regard for the cyclic, internal sequences of the control device. The memories for holding the screen contents appear to the processor system as part of the memory regions directly available to it. Actuation is effected by way of a memory oriented address corresponding to the customary addressing of RAM or ROM memory modules. Access to the memory regions "reserved" for the LCD is here made in regular succession by switching off access by the computer for a short time, it being possible, by means of appropriate buffering between computer and screen memory, that this causes no or at most a slight time delay for the processor system.
In this connection, it is of particular significance that changes of picture contents with slight ch

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patent: 4536856 (1985-08-01), Hiroishi
patent: 4554538 (1985-11-01), Bienemau
patent: 4591850 (1986-05-01), Lundstrom
"Spotlighting display devices: Dot-matrix LCD Modules Finding New and Varied Applicantions", Journal of Electronic Engineering, vol. No. 20, No. 195, Mar. 1983 Tokyo, Shuichi et al, pp. 93-97.

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