JPH01266592A - Image display system - Google Patents

Abstract

PURPOSE:To share one image memory by plural display devices by providing a contention preventing means which allows the image memory to be accessed by other display controllers at the time of receiving a nonselection command to a memory control line which connects display controllers and the image memory. CONSTITUTION:Two display devices are allowed to share one image memory 5 and the memory control lines 23 which connects the two display controllers 2 and single image memory 5 is provided with the contention preventing means which allows the image memory 5 to be accessed by the other display controller 22 at the time of receiving the nonselection command. Thus, the nonselection command is received, the access to the image memory 5 by the other display controller 22 is allowed. Consequently, the display data in the image memory are utilized by the display device 2 without any contention and plentiful image displays are made at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image display system in which an image memory can be shared by a plurality of display devices.

[Prior Art] Information processing devices having a graphic display function, such as those found in personal computers and some word processors, include DSPs, which can speed up the process of transferring image data to a display device compared to software processing. (Di
spray Controller) and CR'1”C
(Cathode Ray Tube Control
A display control device called "ler" is used.

The image display system 1 shown in FIG. 3 includes two display devices 2.
The display control device 3 corresponding to the central processing unit 4 is of a frame buffer type, each having an image memory 5 independent of the central processing unit 4, and the image memory 5 is used only when the display data needs to be changed. Drawing data is transferred from a main storage device (not shown) in the device 4 via the display control device 3 .

Further, the parallel data read from the image memory 5 is converted into serial data by a parallel/serial conversion circuit 6 and sent to the display device 2, and each horizontal and vertical synchronization signal supplied by the display control device 3 is sent to the display device 2. A predetermined rask scan is performed according to the following.

By the way, the display control device 3 mainly includes a control circuit 7 that plays central functions for synchronization generation and drawing, an interface circuit 8 that is involved in exchanging signals with the central processing unit 4, and an image memory 5.
A data buffer circuit 9, etc., which functions as a buffer for data transfer to the display device 2, is connected to the display device 2. Memory control line 1
0 is a general term for address buses, control buses, etc. necessary for writing and reading data to and from the image memory 5. A data bus 11 for drawing data that connects the data buffer circuit 9 and the image memory 5 and a data bus 12 for display data that connects the image memory 5 and the parallel/serial conversion circuit 6 are partially bidirectional buses. Commonly used for drawing data and display data.

Note that the interface circuit 8 has a chip select terminal 8.
By cutting off the supply of the chip select signal to a, it is disconnected from the central processing unit 4, and redundant access by the central processing unit 4 between the plurality of display control devices 3 is prevented.

The problem that this invention tries to solve! i] In the conventional image display system 1, even if the display control device 3 is disconnected from the central processing unit 4 by a chip select signal to the interface circuit 8, the display data necessary for display on the display device 2 is stored in the image memory 5. Therefore, it is impossible to allow another display control device 3 with a different boundary to access this image memory 5 by crossing the border. Since it is not possible to break the correspondence relationship between pairs 1 and 1, multiple display devices 2 cannot freely use the image data stored in the image memory 5, and it is not possible to provide a variety of graphic modes. However, since it requires a large number of image memories 5, there are problems such as a large cost burden.

[Means for Solving the Problems] The present invention solves the above problems, and a display control device provided between a central processing unit and an image memory writes drawing data from the central processing unit to the image memory. and an image display system that controls readout of display data from an image memory to a display device, the memory control line connecting the display control device and the image memory being connected to another display control device when a non-selection command is received. The present invention is characterized in that it is configured by providing a conflict prevention means that allows access to the image memory by the user.

[Operation] The present invention is capable of receiving a non-selection command on a memory control line of a display control device that controls writing of drawing data from the central processing unit to the image memory and reading of display data from the image memory to the display device. In some cases, a conflict prevention means is provided that allows other display control devices to access the image memory, so that a plurality of display devices can use the display data in the image memory without conflicting with each other.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1.2. FIG. 1 is a circuit diagram showing an embodiment of the image display system of the present invention.

The image display system 21 shown in FIG. , when the non-selection command is received, the other display control device 2
2 is provided with a conflict prevention means that allows access to the image memory 5 by the image memory 5. The conflict prevention means shown in the embodiment is configured by connecting a tri-state buffer 24, which fixes the memory control line 23 to high impedance upon receiving a non-selection command, to the image memory 5 through a wired-OR connection. 25 is a wired-OR connection point and an image memory 5
This is a pull-up resistor that connects the memory control line 23 between the terminals and the power supply Vcc.

A tri-state input serving as a non-selection command is provided by a selection circuit 26 connected to the central processing unit 4. In addition, in the embodiment, the non-selection command output from the selection circuit 26 is
In order to use this signal as a signal for disabling the control function of the control circuit 7, the control circuit 7 is provided with an input terminal 7a for inputting a non-selection command.

As is well known, the tri-state buffer 24 can be in three states depending on how the signal is applied to the tri-state input terminal: an on state where the signal is transmitted, an off state where the signal is blocked, and a high impedance state which is a virtual deafness state. It is known to take Therefore, by setting one of the tri-state buffers 24 to a high-impedance state with a non-selection command from the selection circuit 26 and separating it from the circuit, only the remaining tri-state buffer 24 is allowed to access the image memory 5. can do.

As a result, the memory control line 23 is occupied by the control circuit 7 leading to the other tri-state buffer 24, and the display data read from the image memory 5 is transferred to the display device via the parallel/serial conversion circuit 6. Sent to 2. Conversely, by setting the other tri-state buffer 24 in a high impedance state, the memory control line 23 can be made to be occupied by the control circuit 7 communicating with one tri-state buffer 24.

In this way, the image display system 21 controls the memory control of the display control device 22 that controls writing of drawing data from the central processing unit 4 to the image memory 5 and reading of display data from the image memory 5 to the display device 2. Since a conflict prevention means is provided on the line 23 and the structure is configured to allow access to the image memory 5 by another display control device 22 when a non-selection command is received, the display data in the image memory 5 can be displayed without conflicting with each other. A plurality of display devices 2 can be used together, and a rich variety of images can be displayed at a much lower cost than in the conventional image display system 1, etc., in which an image memory 5 is arranged for each display device 2.

In addition, a tri-state buffer 24 that fixes the memory control line 23 to high impedance upon receiving a non-selection command is provided.
Since the contention prevention means is configured by connecting to the image memory 5 through a wired-OR connection, a non-selection command is issued to all but one of the tri-state buffers 24 to multiple display control devices 22 that share the image memory 5. By giving , it is possible to select the display control device 22 that can be accessed, and it is possible to easily and surely eliminate competition.

In the above embodiment, the wired-OR connection circuit of the tri-state buffer 24 is used as the conflict prevention means, but as in the image display system 31 shown in FIG. A conflict prevention means can also be constructed by connecting an OR gate circuit 32 that fixes the control line 23 to a high level to the image memory 5 via an AND gate circuit 33. In this case, by setting all but one of the OR gate circuits 32 to a high level output state for a plurality of display control devices 34 that share the image memory 5, the display control devices 34 that can be accessed
can be selected, making it possible to eliminate conflicts easily and reliably.

Further, in each of the above embodiments, the control circuit 7 in the display control device 22 or 34 is provided with the input terminal 7a for enabling or disabling its control function, but instead of providing this input terminal 7a, The control function of the control circuit 7 may be controlled by instructions (commands) from the processing device 4. In this case, it is preferable to keep a part of the interface circuit 8 in an operating state during the instruction transfer period.

[Effects of the Invention] As explained above, the present invention provides a memory control line of a display control device that controls writing of drawing data from the central processing unit to the image memory and reading of display data from the image memory to the display device. Since the structure is configured such that a conflict prevention means is provided in the image memory to allow another display control device to access the image memory when a non-selection command is received, the display data in the image memory can be shared between multiple display devices without conflicting with each other. can be used together, and has excellent effects such as being able to display a rich variety of images at a much lower cost than conventional image display systems in which an image memory is provided for each display device.

Furthermore, the present invention constitutes a conflict prevention means by connecting a tri-state buffer that fixes the memory control line to high impedance in response to a non-selection command to the image memory through a wired-OR connection, so that the image memory can be shared. By giving a non-selection command to all but one of the tri-state buffers to multiple display control devices, an accessible display control device can be selected, making it possible to eliminate conflicts easily and reliably. It has certain effects.

Furthermore, the present invention constitutes a conflict prevention means by connecting an OR gate circuit that fixes the memory control line to a high level in response to a non-selection command to the image memory via an AND gate circuit. By setting all but one of the OR gate circuits to a high level output state for multiple display control devices that share a common display control device, it is possible to select an accessible display control device and eliminate conflicts easily and reliably. It has the effect that it is possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the image display system of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the image display system of the present invention, and FIG. 3 is a circuit diagram showing a conventional image display system. FIG. 1 is a circuit configuration diagram showing an example of an image display system. 2183 display device, 4. ．． ．． Central processing unit, 5°00 image memory, 21.31. ,,Image display system, 22,
34. ,,display control device,23. ,. Memory control line, 24. ,,) Rice State Babufa, 3
2. ,,OR gate circuit,33. ,,and gate circuit.

Claims (3)

[Claims] (1) An image display system in which a display control device installed between the central processing unit and the image memory controls writing of drawing data from the central processing unit to the image memory and reading of display data from the image memory to the display device. an image display, wherein a memory control line connecting the display control device and the image memory is provided with conflict prevention means that allows access to the image memory by another display control device when a non-selection command is received; system. (2) The contention prevention means is characterized in that a tri-state buffer that fixes the memory control line to high impedance upon receiving a non-selection command is connected to the image memory through a wired-OR connection. The image display system according to scope 1. (3) The conflict prevention means includes an OR gate circuit that fixes the memory control line at a high level upon receiving a non-selection command;
The image display system according to claim 1, wherein the image display system is connected to the image memory via an AND gate circuit.