JPH0451092A - display control circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application 1] The present invention relates to the structure of a register in a display control circuit of a personal computer, workstation, or the like.

[Prior Art J] Conventional display control circuits can be used in a display mode for dot sequential scanning devices such as CRT display devices (hereinafter referred to as CRT mode) and for displaying line sequential scanning devices such as liquid crystal display devices. In the CRT mode (hereinafter referred to as LCD mode), a register that determines the display timing is shared, and the setting value of the register is switched depending on the mode to change the display timing.
Or they could switch to LCD.

[Problem to be Solved by the Invention 1] The conventional display control circuit described above was able to reduce the scale of the circuit, but had the following drawbacks. Namely, the register group of the display control circuit The application software that writes values to the LC and displays windows and graphs was developed for CRT mode, so it cannot be displayed as is and cannot be used in LC mode.
There was a problem in that it was necessary to change the software for D mode.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a display control circuit that allows a huge amount of application software that has already been developed for CRT mode to operate in LCD mode as well.

[Means to solve the problem]

In the display control circuit of the present invention, the value of the register that determines the display timing of a line sequential scan type scan such as an LCD device is
The present invention is characterized by having means for providing the result of an operation using the value of a register that determines the display timing of a dot-sequential scanning device such as a CRT display device.

[For production]

The display device of the present invention configured as described above operates as follows in a mode for driving an LCD device.

The application software programmed for CRT mode is a microprocessor (hereinafter referred to as MPU).
The values necessary for display operation are set in the CRT mode V register of the display control circuit through. The arithmetic circuit in the display control circuit performs necessary arithmetic operations on the value of the CRT mode register according to the type of register, and sets the value in the LCD mode register. The LCD timing generation circuit uses this value to
Since the timing for CD is generated, the LCD operates normally with software for CRT.

〔Example〕

Hereinafter, the present invention will be described in detail based on Examples.

FIG. 1 is a block diagram of a display control circuit according to an embodiment of the present invention.

2 is a display control circuit of the present invention, 2 is a CRT display device, and 3 is an LCD display device.

In this embodiment, a CRT display device is used as an example of a dot sequential scanning type display device, and an LCD display device is used as an example of a line sequential scanning type display device.

Before explaining the operation of the embodiment, first, the difference in display timing between CRT and LCD will be described. The CRT uses an electron beam to scan from the upper left to the lower right of the display, repeating horizontal scanning and also vertical scanning, to complete the display of one screen. On the other hand, in order to improve the display contrast of an LCD, due to its physical structure, the screen is divided into upper and lower halves, and display data is controlled independently of the upper and lower halves. For this reason, it is necessary to transfer data for a total of 2 lines of 1 line for the upper and lower users during the horizontal scanning time, and CR
Compared to T, the number of display dots in the horizontal scanning time is doubled, and conversely, the number of lines in the vertical scanning time is 1/2. This is shown in Figure 2. Figure 2 (a) is a CRT display, Figure 2 (b)
) are LCD displays, where the shaded area is the display area and the blank area is the retrace period.

A general-purpose display control circuit has many register groups so that it can support displays of various resolutions, character display modes, and graphics display modes. CRT and LCD mentioned above
Due to the difference in , many of these registers need to have different values in CRT mode and LCD mode. The embodiment of the present invention shown in FIG. 1 will be explained by taking as an example a register that determines the total number of horizontal characters and the total number of vertical characters.

Application software 12 programmed for CRT sets necessary values in registers in display control circuit l through microprocessor 13. The value is given to the data bus, and the address decoder 17, which receives the address bus and control bus as input, outputs the write control signal /WRA1.
5 is generated and the value is written to the horizontal pictographic register 4 for CRT. When displaying on the CRT display device 2, the CRT timing generation circuit 1
0 outputs the horizontal synchronizing signal H3YNC and performs horizontal scanning of the CRT.

On the other hand, as is clear from the difference between CRT and LCD mentioned above,
When displaying a CD, horizontal scanning must be performed at twice the frequency. Therefore, the x2 arithmetic circuit 5 doubles the value of the horizontal total character register for CRT and sets it in the character register 6 for LCDCD. The LCD timing generation circuit 11 outputs the horizontal scanning line latch signal LP according to the doubled set value.

Regarding vertical scanning, since both the CRT and LCD are driven at approximately the same frame frequency, the number of vertical lines in the LCD mode is 1/2 compared to the CRT mode.

Therefore, the ÷2 calculation circuit 8 sets the value of the vertical total character register for CRT to the vertical total character register 9 for 1/2LLCD,
The LCD timing generation circuit generates a frame start pulse YD at a cycle based on this value.

As explained above, even if the CRT application software sets the CRT registers while the LCD display device is connected to the display control circuit, the display control circuit of the present invention will not perform the necessary calculations. Since the value is set in the display register of the LCD, normal display can be performed.

On the other hand, in the conventional display control circuit shown in Fig. 3, a register is shared between CRT mode and LCD mode, and different values are set in the register for each mode to switch which mode the timing generation circuit operates in. Met. Therefore, it was not possible to display the LCD using application software for CRT mode, and it was necessary to develop software for the LCD.

[Effects of the Invention] In recent years, portable personal computers such as laptop-type devices using LCDs for display have been developed and are now widely used. However, the software is
It was for display purposes and required software development.

According to the present invention, the value of the register that determines the display timing of the LCD display device is given as a calculation result using the register value that determines the display timing of the CRT display device, so there is no need to develop software for the LCD. ,
This has the advantage that LCD display can be performed using existing CRT software. Furthermore, as can be seen from the comparison between FIG. 1 and FIG. 3, it also has the effect of allowing simultaneous display on the CRT and LCD.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a display control circuit according to the present invention. FIGS. 2(a) and 2(b) are diagrams showing the difference between CRT display and LCD display. FIG. 3 is a schematic diagram of a conventional display control circuit. l ・ ・ ・ 2 ・ ・ ・ 3 ・ ・ 4, 7 ・ 5, 8 ・ 6, 9 ・ X O ・ ・ 1 l ・ ・ ・ Display control circuit CRT display device LCD display device CRT register operation circuit for LCD Register CRT timing generation circuit LCD timing generation circuit Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (and one other person) Figure 2

Claims (1)

[Claims] It has a register that determines display timing and a timing circuit that generates a timing signal according to the value of the register, and uses the timing signal to perform both a dot sequential scanning type display device and a line sequential scanning type display device simultaneously or by switching. The display control circuit capable of displaying a display device is characterized by having means for providing a value of a register that determines the timing of a line-sequential scanning type display device as an operation result using the value of the register that determines the timing of the point-sequential scanning type. display control circuit.