Microcontroller with internal clock for liquid crystal display

Details Microcontroller with internal clock for liquid crystal display Microcontroller with internal clock for liquid crystal display

1996-06-28

2002-01-15

Shalwala, Bipin (Department: 2673)

Computer graphics processing and selective visual display system

Plural physical display element control system

Segmented display elements

C345S213000

Reexamination Certificate

active

06339413

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to co-pending applications titled “Microcontroller with Dual Port RAM for LCD Display and Sharing of Slave Ports”, “Microcontroller with LCD Control over Updating of Ram-Stored Data that Determines LCD Pixel Activation”, “Microcontroller with Liquid Crystal Display Charge Pump”, and “Methodology for Testing a Microcontroller Chip Adapted to Control a Liquid Crystal Display”, filed on the same day and assigned to the same assignee as this application, and the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to microprocessors especially adapted to provide control functions for external systems or subsystems, and thus generally referred to as microcontrollers, and more particularly to microcontrollers which are capable of providing liquid crystal display (LCD) driver functions without need for peripheral elements other than the display itself.
An LCD generally comprises a pair of glass plates between which a liquid crystal material is sandwiched, the liquid crystal having the property of undergoing orientation of its crystal-like structure according to an electric field placed between transparent electrically conductive material on the plates, and thereby causing a selective darkening of the respective pixels with the passage of light through the liquid crystal to render the darkened pixels visible to the eye. The typical LCD, such as that shown in
FIG. 1
, which illustrates a panel
10
of the prior art, employs a plurality of commonly formed, potential alphanumeric characters
12
. Each ofthe characters is in the form of a block figure “8” shape composed of a plurality of individual lineal pixels
15
—typically seven as shown in the Figure, although more may be used where greater curvature or detail of reproduction of the particular alphanumeric character to be displayed is desired. In the seven pixel character, three horizontal pixels such as
17
,
18
, and
19
are vertically aligned and equally spaced apart, and two vertical aligned pixels
21
,
22
(and
23
,
24
) are positioned at each end of the array of horizontal pixels bounding the respective spaces between the latter.
The pixels are conventionally driven by waveforms applied to a digitally encoded array of electrical conductors of printed circuit form (not shown in FIG.
1
), each of the conductors on the top side of the LCD being connected to “segments”, while the conductors on the bottom are connected to “commons”. Hence, when a particular digital code (e.g., binary-based) is applied in the form of an electrical energization of the various conductors, a particular alphanumeric character is displayed on the LCD—assuming, of course, the presence of a source of light emanating through the plates. The “segments” are electrically energized by drivers which are supplied as part of a peripheral device, typically on a semiconductor circuit chip (not shown in FIG.
1
). The “commons” are also driven by the semiconductor circuit chip in such a way that the RMS voltage across each of the pixels will be either above a threshold value (pixel dark) or below that threshold value (pixel clear). For any given LCD, the product of the number of “commons” multiplied by the number of “segments” is equal to the number of pixels in the display.
LCDs are used in a wide variety of applications including home security systems, industrial control thermostats, home thermostats, blood pressure meters, blood glucose meters, AC power meters, toys, voice recorders, microwave ovens, and carbon monoxide detectors, to name but a few. The use of LCDs in such applications, and in which one or more microcontrollers is used to control the system constituting the application in which the LCD is used, is, in and of itself, quite conventional. Heretofore, however, the display (which may include a large number of pixels) has been operated and controlled by its own power source and control devices, while the system in which or with which the display is used is separately controlled by the microcontroller. The requirement of separate control devices has adversely affected the cost, complexity, and size of the overall control portion of the system.
The nature of the problem may be better understood by reference to a relatively simple example of a thermostat which is used to control the temperature of the air in an enclosure by means of control exercised on a heating, ventilating, and air conditioning (HVAC) system for the enclosure. A thermistor provides an analog input indicative of the temperature of the air in the enclosure. An LCD display provides a visual indication of that temperature, and also displays a set point or set temperature which is designated by the user by appropriate selection using a keypad. An interrupt is provided by a keypad interface that allows the user to punch in certain keypad information as references which are used by the microcontroller to change the display, such as to write another output into memory—a select voltage for the thermostat output at which the microcontroller will turn on a heat pump in the system.
It would be desirable to consolidate everything, or at least a substantial part of the control functions, within a single product—namely, the microcontroller chip itself. Such a goal, however, is by no means a simple task. An LCD display operates at a considerably slower speed than a microcontroller. Also, the timing of the microcontroller control functions is different from the timing of the LCD control functions. Another issue arises in connection with the capability of a microcontroller to be placed in a “sleep” mode or sleep state to conserve power, whereas the LCD display must continue to function.
Present-day systems that control an LCD display which itself is used in conjunction with a system to be controlled by a microcontroller require a source of clock pulses to control the timing and updating of the display, among other things, when not supplied by the microcontroller itself, as when the latter is in its sleep mode. Although the microcontroller device package typically has a pin available for an external input, the device user may not wish to use that capability, preferring to reserve it for other essential purposes. For the LCD to remain operational, the timing module must supply clock signals to the logic section which drives the LCD display. In a typical present-day application, currently available microcontrollers are incapable of providing any clock function when in the sleep state.
If the device user's application requires that the LCD display must or should remain operational, it becomes necessary for the user to employ a separate device that will make external clock signals available for LCD control, by applying the external clock to an external pin of the microcontroller. This means that the selected pin (only a finite number of which are available—in a typical device, only one, or perhaps two) will be unusable for another purpose. And the other purpose may be much more essential in an emergency situation.
Two types of waveforms are variously used to drive an LCD display, as will be described in greater detail below. A type A waveform generates “common” and “segment” waveforms, with all data contained in a single frame and assembled in complementary fashion, such as high voltage and low voltage, to produce a DC value of zero for that frame. It is essential that the voltage waveform across the glass plates of the display be maintained at an average DC value of zero because the glass is likely to suffer a breakdown if a non-zero DC voltage is applied for any sustained period of time. A type B waveform generates “common” and “segment” waveforms with ,all of the data in two frames, the actual data being assembled in a first frame and that same data being assembled in inverse form in a second frame, such that an average DC value of zero is maintained for the type B waveform over a full two frames of data.
Generally, the type A waveform is employed for si

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