KR100568696B1 - Character scrolling method and apparatus - Google Patents

Abstract

Disclosed are a method of scrolling a text line on a display screen of a text liquid crystal display, and an apparatus therefor. When a vertical scroll command is issued, in response to each frame period, the data to be displayed on the first character line is displayed at a fixed position of the first character line. Data to be displayed from the second character line to the last character line is displayed by scrolling vertically by the number of scan lines designated by the vertical scroll command. For such scrolling, the state change of the count value of the line counter is controlled. The state change of the count value for the first character line is controlled to be in a fixed order, but the state change of the count value for the second character line to the last character line is controlled to vary according to a predetermined sequence. The line counter applies a driving signal to the scan line of the display screen corresponding to the count value in synchronization with the state change cycle of the count value. The scan line driving signal is combined with a driving signal for character data applied to a vertical line of the display screen to provide driving information of the display screen.

Description

Character scrolling method and device {CHARACTER SCROLLING METHOD AND APPARATUS}

1 is a block diagram showing a circuit configuration of a character scrolling device according to an embodiment of the present invention.

2A to 2C show the relationship between the screen display and the count value LINE of the line counter when the first character line is fixed, and the second and second character lines are scrolled up and down by two dots. .

3 is a flowchart showing a state change of a line counter defining an application sequence of a scan line driving signal to a scan line.

4 is a flowchart illustrating a state change of the variable START2 that defines a scroll initial value as a state variable of the line counter.

5 is a flowchart illustrating a state change of the variable END that defines a scroll end value as another state variable of the line counter.

6 shows a state in which the count value of the line counter changes for scrolling up and scrolling down.

<Description of Symbols for Main Parts of Drawings>

100: MPU interface unit 102: address counter

104: scan counter 106: line counter

108: display data RAM 110: character generation ROM

112: shift / latch register 114: shift register

116: vertical line driver 118: scan line driver

120: system clock 122: microprocessor unit

124: LCD panel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scrolling method and apparatus for an image display device. In particular, the character data displayed in the display of graphic characters by a dot matrix method such as a liquid crystal display device (hereinafter referred to as "LCD") is vertically aligned. The present invention relates to a method for scrolling and an apparatus therefor.

As portable communication devices such as cellular phones or personal communication service (PCS) phones become more advanced, the types and quality of services provided by communication service providers are changing. For example, data such as weather information, stock information, or traffic information is provided through a display screen of a portable communication device. Such services have gained much attention in that users can obtain desired information on the fly. The device having the display screen is not limited to only portable communication devices. For example, liquid crystal displays (LCDs) are also employed in portable audio playback devices such as cassette tape recorders, CD players, and MPEG-3 players, which have become popular in recent years. Such an apparatus also has an example of additionally including a function of displaying information on data to be reproduced, for example, song names, lyrics, and other information, on a display screen.

The information provided usually consists of a title and its contents. Depending on the type of information, a single title may contain a large amount of data. When the above information service is received through a device employing a large display screen, the display screen may be displayed at once without scrolling up and down. However, in general, the display screen employed in the portable device is made small in order to meet the miniaturization of the device. Therefore, there is a need for a method capable of displaying a large amount of data at once on such a small display screen.

One way to meet these needs is image scrolling technology. However, the conventional image scrolling method scrolls the entire screen up and down without distinguishing between the title and the content of the service information. According to this scrolling method, after the scrolling has been progressed for some time, the title disappears from the screen and only the contents are displayed. Since the title and its contents do not appear on the display at the same time, it is not possible to know what title the data displayed on the screen is related to. It is an object of the present invention to propose a method for eliminating such inconvenience.

Accordingly, an object of the present invention is to provide a graphic character scrolling method for displaying a graphic character data on a display screen so that only the content belonging to the title is scrolled without the title being scrolled.

Another object of the present invention is to provide a graphic character scrolling device capable of executing the graphic character scrolling method as described above.

In order to achieve the first object, the image scrolling method according to the present invention includes C character lines spaced in the vertical direction, and each character line has N scan lines spaced in the vertical direction and in the horizontal direction. A display screen having M vertical lines spaced apart from each other, and the graphic character data provided to the M vertical lines is applied to the graphic character display device such that only the scan lines to which the scan line driving signal is applied are displayed. The scrolling method controls the application sequence of the scan line driving signal to scroll the graphic characters on the display screen. Specifically, it is detected whether a vertical scroll command is applied. In response to the vertical scroll command being applied, the data to be displayed on the first text line is displayed at a fixed position of the first text line every frame period, and the data to be displayed on the first text line from the second text line is Scrolls and displays vertically by the number of scan lines specified by the vertical scroll command.

When the vertical scroll command instructs scroll up, the number of scan lines to which the scan line driving signal is applied is 0, 1, 2, ..., N-1, (N-1) + J, ( N-1) + J + 1, (N-1) + J + 2, ..., C * N-1, SC_LINE_NO. Here, the value of the variable J is increased by the number of scan lines for each frame period, and the variable SC_LINE_NO is a sequential set of natural numbers larger than 'N-1' and smaller than '(N-1) + J'.

In addition, when the vertical scroll command instructs scroll down, the number of scan lines to which the scan line driving signal is applied is 0, 1, 2, ..., N-1, SC_LINE_NO, N, N + 1 , N + 2, ..., C * NJ. Here, the value of the variable J is increased by the number of scan lines for each frame period, and the variable SC_LINE_NO is a sequential set of natural numbers larger than 'C * N-J' and smaller than 'C * J'.

Accordingly, scan lines belonging to the first character line are sequentially enabled from scan line number 0 to N-1 in every frame period. Thus, the image for the first character line is displayed at a fixed position in each frame period. However, the scan lines belonging to the second character line to the last character line are cyclically changed in the enabled order as the variable J sequentially increases from 1. The cyclical change of the enable order causes the text data of the second to last text lines on the display screen to be scrolled up or down vertically.

In order to achieve the second object of the present invention, the image scrolling device according to the present invention comprises C character lines spaced in the vertical direction, each character line having N scan lines spaced in the vertical direction and also horizontal A display screen having M vertical lines spaced in the direction is provided. The scan line driver circuit applies the scan line drive signal to the scan line specified by the scan line number, and the vertical line driver circuit applies the vertical line drive signal to the vertical line specified by the character data. Character data providing means provides the vertical line driver circuit with the character data to be displayed on the display screen every scan line period. The counting means, in response to the vertical scroll command, displays the data to be displayed on the first text line at a fixed position of the first text line, and the data to be displayed on the first text line from the second text line. The scan line number is counted so as to scroll in the vertical direction by the number of scan lines specified by the vertical scroll command, and provided to the scan line driver circuit.

The display screen may be a liquid crystal display (LCD) as an example. However, the present invention can be applied to any display screen formed by connecting a dot matrix pixel array to a driving line such as a scan line and a vertical line intersected in a matrix.

When scroll-up is instructed, the data displayed on the first text line is displayed at a fixed position, but the data displayed on the second text line to the last text line is displayed by moving up a predetermined number of scan columns every frame period. . To this end, the counting means sets the scan line number to 0, 1, 2, ..., N-1, (N-1) + J, (N-1) + J + 1, (N-1) + J. Outputs counting in order of +2, ..., C * N-1, SC_LINE_NO. The value of the variable J is increased by the number of scan lines every frame period, and the variable SC_LINE_NO is a sequential set of natural numbers larger than 'N-1' and smaller than '(N-1) + J'.

On the contrary, when the scroll down is instructed, the counting means sets the scan line number to 0, 1, 2, ..., N-1, SC_LINE_NO, N, N + 1, N + 2, ..., C * NJ Counting output. The value of the variable J is increased by the number of scan lines every frame period, and the variable SC_LINE_NO is a sequential set of natural numbers larger than 'C * N-J' and smaller than 'C * J'.

The graphic character scrolling device provides the character data to be displayed and the address thereof to the character data providing means, and controls the counting means to count according to the counting sequence corresponding to the indicated scroll mode in response to a user's scroll instruction. It further comprises a control means.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

First, FIG. 1 shows a circuit configuration of a graphic character scroll device according to an embodiment of the present invention. The microprocessor unit (hereinafter referred to as 'MPU') 122 loads the data to be displayed on the LCD panel 124 to the display DRAM 108 through the MPU interface unit 100 and simultaneously displays an address value for the data. The address counter 102 is provided. The address counter 102 generates address information of the display DRAM 108 in which the data provided by the MPU 122 is to be recorded as an address counter for the display DRAM 108. That is, the MPU 122 accesses the display DRAM 108 through the address counter 102 to load the data. The display DRAM 108 stores the address of the font data of the character generation ROM 110 to be displayed on the LCD panel 124. Therefore, the MPU 122 writes data to the display DRAM 108 to designate the character to be actually output. The character generation ROM 110 is a place where font bitmap data, which is actual data of a character, is stored. The character generation ROM 110 is formed by combining an address provided by the scan counter 104 and an address provided by the line counter 106. ) Is used as the address (ROM_ADDR).

The scan counter 104 sequentially reads data stored in the display DRAM 108 and provides the character generation ROM 110 with an address corresponding to the read data. In this case, the scan counter 104 counts the scan clock SCAN_CK provided from the system clock unit 120 to read the display DRAM 108 at a scan line period.

The line counter 106 receives the line clock LINE_CK provided from the system clock unit 120 and counts the scan line value currently displayed on the LCD panel 124. The scan line value counted by the line counter 106 generally increases sequentially with the scan line period.

However, for vertical scrolling according to the present invention, an arbitrary change of the counting value is required in the counting process. The first character line in which the title is displayed should not be scrolled, but from the second character line in which the content is displayed.

First, the scan line value at which data corresponding to the second character line should be displayed for the first time needs to be variably set. For this purpose, immediately after counting the scan line corresponding to the first character line in a normal manner, the counting value LINE of the line counter 106 is forcibly changed. After the counting value is set to another value, the line counter 106 newly performs sequential counting from the changed value. Furthermore, after the counting value becomes equal to the final value, that is, the last scan line number MAX, it may be changed to a predetermined designated value. Several registers are used to control this counting schedule. The first register (not shown) that defines the initial value, that is, the first scan line value of the first character line, the start count value (scroll start value) and the last count value (scroll end value) for the second to last character lines. It is the second and third registers (not shown) that respectively define. These registers may be registers basically provided to the MPU 122, or may be configured separately in addition to the line counter 106.

The counting value of the line counter 106 is output for each scan line period. The output value COM_DATA is used for specifying the address of the character generation ROM 110 together with the address output by the scan counter 104 as mentioned above, and also controls for generating the scan line driving signal COM_OUT. It is also loaded into the shift register 114 which generates a signal.

The character generation ROM 110 receives the combined address ROM_ADDR of the scan counter 104 and the recounter 106 and periodically outputs one scan line of character data corresponding to the address. The output character data is loaded into the register 112. When character data is output in a bitstream form, for example, the register 112 is configured as a shift / latch register. When all character data of one scan line is loaded, the register 112 applies the loaded character data to the LCD driver 116. The LCD driver 116 decodes the applied character data and applies the driving signal SEG_OUT to a vertical line of the LCD panel 124, that is, a segment line.

In parallel with this, the shift register 114 also applies the output data COM_DATA of the line counter 106 to the LCD driver 118 every scan line period. The LCD driver 118 decodes the output data COM_DATA and applies the driving signal COM_OUT to a row line of the LCD panel 124, that is, a scan line.

The LCD panel 124 selectively emits only pixels to which the segment line driving signal SEG_OUT and the scan line driving signal COM_OUT are simultaneously applied to display a designated character.

In the character type liquid crystal display device having such a configuration, the vertical scroll of the character data displayed on the LCD panel 124 can be implemented by variably adjusting the output value COM_DATA of the line counter 106. Assume that the LCD panel 124 has four character lines and each character line has 16 scan lines, that is, a case in which there are 64 scan lines in total. When the output value COM_DATA is generated when the count value LINE of the line counter 106 is other than 0, for example, the count value LINE is 2, the font data of the second scan line is displayed in the LCD driver 116. When the first scan line is enabled, the form displayed on the LCD panel 124 appears as if it is scrolled up by 2 scan lines as shown in FIG. 2B. In contrast to scroll down, if the line counter 106 generates the output value COM_DATA when the count value LINE is 62, the character data displayed on the LCD panel 124 is as shown in Fig. 2C. It will look as if it has scrolled up by 2 scan lines.

By applying the vertical scroll principle, it is possible to selectively scroll only the desired text lines. For example, consider a method of fixing the first text line and selectively scrolling only the second text line to the last text line. Here, it is assumed that the above conditions for the size of the LCD panel 124 are the same. For the scan line numbers 0 to 15 (the first character line), the count value (LINE) should be increased sequentially from 0 to 15, but the scan line numbers 16 to 63 (the second character line to the last character line) will be increased. For example, if the count value LINE is varied as necessary, the display position of the character data of the first character line is fixed, whereas the character data of the remaining character lines is displayed as if the displayed position is moved up and down.

3 is a flowchart illustrating a state change of the line counter 106 to implement a function of fixing the text data of the first text line and vertically scrolling the data of the second to last text lines.

First, in the first state of displaying text data of one frame, the line counter 106 is initialized to an initialization value START1, that is, 0, provided from the first register (step S10). Subsequently, the line counter 106 counts the line clock LINE_CK and increments by one until the count value LINE reaches 16 (steps S12 and S14). When the count value LINE reaches 16, the value changes to the scroll start value START2 provided from the second register (step S16). When the count value LINE is equal to the scroll end value END provided from the third register, the count value LINE is fed back to the step of setting the initialization value START1 (step S10) (step S18). When the count value LINE is not equal to the scroll end value END, it is compared with the last scan line number MAX (63 in the above assumption) (step S20). If the comparison result is true, the count value (LINE) is forced to 16. If the comparison result is true, the count value (LINE) is increased by 1, and then again the count value (LINE) is equal to the scroll end value (END). It is fed back to the step S18 to determine.

In order to display the character data of the first character line at a fixed position, the initialization value START1 should always be a fixed value, that is, zero. However, the start point and end point of the scan line to be scrolled, that is, the scroll start value START2 and the scroll end value END, should be regularly changed to different values for each frame period.

4 is a flowchart showing a change state of the scroll start value START2. The scroll start value START2 is changed every frame period according to the following rules, and the change of the scroll start value START2 affects the counting value LINE of the line counter 106 (S16). Step) The character data displayed in the second character line to the last character line is scrolled in a predetermined sequence.

The scroll start value START2 is set to 16, which is the first scan line number of the second character line until scrolling starts (step S30). Subsequently, it is detected whether a scroll command is applied to determine whether to indicate scroll up or scroll down (step S32).

When the scroll up is instructed, it is checked whether the scroll start value START2 is equal to the last scan line number MAX (step S34). If the test result is true, the scroll start value START2 is forced to 16 (step S36), but if it is false, 1 is increased (step S38). After the above process, the process is fed back to step S32 to determine the type of the scroll command.

On the other hand, if it is determined that the scroll down is instructed (step S32), it is checked whether the scroll start value START2 is equal to 16 (step S40). If the check result is true, the scroll start value START2 is set to 63, which is the last scan line number MAX (step S42), and if false, the scroll start value START2 is decremented by 1 (step S44). ). After the above process, the flow is fed back to the step of determining the type of the scroll command (step S32).

5 is a flowchart showing a change state of the scroll end value END. Similar to the scroll start value START2, the scroll end value END changes its value every frame period according to the following rules. The scroll end value END, together with the scroll start value START2, affects the counting value LINE of the line counter 106 (step S18), which is displayed in the last character line from the second character line. The character data is scrolled according to a predetermined sequence.

First, until the scroll starts, the scroll end value END is set to 63, which is the last scan line number MAX. Subsequently, it is detected whether a scroll command is applied to determine whether to indicate scroll up or scroll down (step S52).

If scroll up is instructed, it is checked whether the scroll end value END is equal to the last scan line number MAX (step S54). If the test result is true, the scroll end value END is forced to 16 (step S56), but if it is false, 1 is increased (step S58). After the above process, the process is fed back to the step of determining the type of the scroll command (step S52).

On the other hand, when it is determined that the scroll down is instructed (step S52), it is checked whether the scroll end value END is equal to 16 (step S60). If the check result is true, the scroll end value END is set to 63, which is the last scan line number MAX (step S62), and if false, the scroll end value END is decremented by 1 (step S64). ). After the above process, the flow is fed back to the step of determining the type of the scroll command (step S32).

FIG. 6 shows the change state of the count value LINE of the line counter 106 according to FIGS. 3 to 5.

When the scroll command is not applied, the count value LINE is changed in the order of '0, 1, ..., 15, 16, ..., 63' and is repeated in every frame period.

When the scroll up command is applied, the count value LINE is changed in the order of '0, 1, ..., 15, 17, 18, ..., 63, 16' in the first frame period. The two frame periods are changed in the order of '0, 1, ..., 15, 18, 19, ..., 63, 16, 17'. The third frame period is changed in the order of '0, 1, ..., 15, 19, 20, ..., 63, 16, 17, 18'. In this way, the change state of the count value changes every frame period.

The change order of the count value LINE when the scroll down command is applied is as follows. That is, the first frame period is changed in the order of '0, 1, ..., 15, 63, 16, 17, ..., 62', and the second frame period is' 0, 1, ..., 15, 62, 63, 16, 17, ..., 61 'in order. The third frame period is changed in the order of '0, 1, ..., 15, 61, 62, 63, 16, 17, ..., 60', and is changed in the same manner for the subsequent frame period.

Generalizing this can be summarized as follows. First, the LCD panel 124 used as the display screen includes C character lines spaced in the vertical direction, and each character line has N scan lines spaced in the vertical direction and M lines spaced in the horizontal direction. Suppose you have a vertical line.

When the vertical scroll command instructs scroll up, the number of scan lines to which the scan line drive signal COM_OUT is applied is' 0, 1, 2, ..., N-1, (N-1) + J , (N-1) + J + 1, (N-1) + J + 2, ..., C * N-1, SU_NO '. Here, the value of the variable J is increased by, for example, 1 by the specified value for each frame period, and the variable SU_NO is a sequential set of natural numbers larger than 'N-1' and smaller than '(N-1) + J'. The initial scroll value (START2) is determined by a relation such as START2 = (N-1) + J, and the scroll end value (END) is equal to the maximum value among the natural numbers belonging to the set variable SU_NO. It can be seen that it is defined variably according to the change of the value of J.

On the other hand, when the vertical scroll command instructs the scroll down, the number of scan lines to which the scan line driving signal COM_OUT is applied is' 0, 1, 2, ..., N-1, SD_NO, N, N + 1, N + 2, ..., C * N-J '. Herein, the value of the variable J is increased by, for example, 1 by the specified value for each frame period, and the variable SD_NO is a sequential set of natural numbers larger than 'C * N-J' and smaller than 'C * J'. Therefore, the scroll initial value START2 is equal to the minimum value among the natural numbers belonging to the set variable 'SD_NO', and the scroll end value END is defined by a relation such as END = C * NJ, and these two values are also variables. It can be seen that it is defined variably according to the change of the value of J.

Meanwhile, the MPU 122 periodically loads an initialization value START1, a scroll start value START2, and a scroll end value END for each of the first to third registers every frame period, thereby counting the count value as described above. Enables status control of the line.

In the above description, a method of fixing the first text line and selectively scrolling only the second text line to the last text line has been described. However, those skilled in the art related to the present invention may apply the above disclosure to various changes of the scroll method. It will be easy to implement. For example, if the title is displayed in the last character line, the fixing of the last character line and scrolling the remaining rub lines are one example of an application. If the change state of the count value (LINE) described above is implemented in reverse, do.

As can be seen from the above description, the present invention allows the first character line where the title is displayed on the dot matrix display screen to be displayed at a fixed position and the contents related to the title can be scrolled up and down. In particular, when it is usefully applied to a portable device employing a small display screen, the user may not feel a great inconvenience even when viewing a large amount of information through the small display screen. Furthermore, the present invention can be applied in various ways regardless of the size of the display screen.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the present invention without departing from the spirit and scope of the invention described in the claims below. I can understand that you can.

Claims (12)

And a display screen having C scan lines spaced in the vertical direction, each scan line having N scan lines spaced in the vertical direction, and having M vertical lines spaced in the horizontal direction. The graphic character data provided as a line is scrolled through the graphic character on the display screen by controlling the order in which the scan line driving signal is applied by using a graphic character display device which displays only the scan line to which the scan line driving signal is applied. In the method, Detecting whether a vertical scroll command is applied; And In response to the vertical scroll command, every frame period, the data to be displayed on the first text line is displayed at a fixed position of the first text line, and the data to be displayed on the second text line from the second text line is the vertical scroll command. And scrolling in the vertical direction by the designated number of scan lines. The method of claim 1, wherein when the vertical scroll command instructs scroll up, the number of scan lines to which the scan line driving signal is applied is 0, 1, 2, ..., N-1, (N−). 1) + J, (N-1) + J + 1, (N-1) + J + 2, ..., C * N-1, SU_NO, where the value of the variable J is for each frame period The variable SU_NO is increased by a predetermined value, and the variable SU_NO is a sequential set of natural numbers larger than 'N-1' and smaller than '(N-1) + J'. The method of claim 1, wherein the number of scan lines to which the scan line driving signal is applied is 0, 1, 2, ..., N-1, SD_NO, N when the vertical scroll command indicates scroll down. , N + 1, N + 2, ..., C * NJ, wherein the value of the variable J is increased by a predetermined value for each frame period, and the variable SD_NO is larger than 'C * N-J'. Graphic character scrolling method characterized by a sequential set of smaller natural numbers than 'C * J'. The method of claim 1, wherein the number of scan lines specified by the vertical scroll command is one. A display screen including C character lines spaced in the vertical direction, each character line having N scan lines spaced in the vertical direction and M vertical lines spaced in the horizontal direction; A scan line driver circuit for applying a scan line drive signal to the scan line specified by the scan line number; A vertical line driving circuit for applying a vertical line driving signal to a vertical line designated by character data; Text data providing means for providing the vertical line driving circuit with the text data to be displayed on the display screen every scan line period; And The scan line value displayed on the display screen is counted, and in response to the vertical scroll command, the data to be displayed on the first text line is displayed at a fixed position of the first text line every frame period, and the second text line is displayed. And counting means for counting the scan line number so as to scroll in the vertical direction by the number of scan lines specified by the vertical scroll command, and providing the data to the scan line driver circuit. Graphic character scroll device. 6. The apparatus according to claim 5, wherein the counting means is 0, 1, 2, ..., N-1, (N-1) + J, (N-1) when the vertical scroll instruction instructs scroll up. The scan line number is counted in the order + J + 1, (N-1) + J + 2, ..., C * N-1, SU_NO, wherein the value of the variable J is a predetermined value for each frame period. Increased by the variable SU_NO is a sequential set of natural numbers greater than 'N-1' and less than '(N-1) + J'. 6. The method of claim 5, wherein the counting means is 0, 1, 2, ..., N-1, SD_NO, N, N + 1, N + 2, when the vertical scroll command indicates scroll down. .., counting the scan line numbers in the order of C * NJ, wherein the value of the variable J is increased by a predetermined value for each frame period, and the variable SD_NO is larger than 'C * N-J' and is 'C *'. Graphic character scrolling device characterized in that the sequential set of smaller natural numbers than J '. The apparatus of claim 5, wherein the display screen is a liquid crystal display screen (LCD). 6. The apparatus of claim 5, further comprising: control means for providing the character data to be displayed and an address thereof to the character data providing means, and controlling the counting so that the counting means corresponds to the indicated scroll mode in response to a user's scroll instruction. Graphic character scroll device, characterized in that provided. The display apparatus according to claim 5, wherein the text data providing means comprises: a display DRAM for storing an address of text data displayed on the display screen; An address counter for providing an address of the data to be written to the display DRAM; A scan counter that sequentially reads the text data stored in the display DRAM and outputs an address corresponding to the read text data; A character generation rom which stores bitmap data relating to a character font and outputs bitmap data of a character font indicated by an address determined by a combination of an output value of the scan counter and an output value of the counting means; And a shift / latch register for temporarily storing the bitmap data output from the character generation ROM and applying the bitmap data to the vertical line driver circuit at predetermined intervals. The method according to claim 5, wherein the counting means increments a count value by counting a line clock signal, and in particular, the count value is sequentially increased from an initial value to a predetermined value, and then the scroll end is performed by counting from the initial value of scroll. A line counter sequentially increasing in value; And a shift register for temporarily storing a count value output from the line counter and applying the count value to the scan line driver circuit. 12. The method of claim 11, wherein the counting means comprises: a first register for temporarily storing the initialization value; A second register for temporarily storing the scroll initial value; And a third register for temporarily storing the scroll end value.

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