JPH083703B2 - Screen display - Google Patents

Description

The present invention relates to a screen display device for displaying characters, patterns, etc. on a display device such as a cathode ray tube.

[Conventional technology]

The screen display device displays characters and patterns on a display device such as a cathode ray tube, and FIG. 4 shows an example of the configuration of a conventional screen display device of this type.

In FIG. 4, reference numeral 1 is an oscillation circuit, 2 is a timing generator that generates various timings with signals oscillated by the oscillation circuit 1, and 3 is an output of the timing generator 2 and a microcomputer for controlling the screen display device. Control data (commands such as display on / off and character codes) 21 of the input control circuit, 4 is a display memory for storing control data, and 5 is a character ROM for storing characters or patterns to be displayed. , 6 is a sync signal input circuit for inputting the sync signal 22 of the video signal, 7 is a display position detection circuit for detecting the display position of characters, patterns, etc., 8
Is a display control circuit, and this screen display device is composed of the above circuits. The output of the display control circuit 8 is output as a display character output 23 to a display device such as a cathode ray tube.

Next, the operation will be described. The input control circuit 3 processes control data 21 from a microcomputer or the like and turns on or off the entire screen display device according to a command such as display on / off. The character code and the like are stored in the display memory 4. The display memory (RAM) 4 needs to write control data and read at the time of display, and the number of read and write addresses increases as the screen display device increases in size (higher functionality). It is advantageous to share the read and write addresses by time division control in order to downsize the circuit configuration. Hereinafter, the description will be continued assuming that writing and reading are time-division controlled.

At the time of display, the output data stored in the display memory 4 accesses the character ROM 5, and the display character output from the character ROM 5 is input to the display control circuit 8. Here, at the display timing, the display position is determined by inputting the sync signal 22 from the video signal to the sync signal input circuit 6 and counting the sync signal by the display position detection circuit 7.

The display control circuit 8 causes the display character output to be output in synchronization with an external video signal and sends it to a display device such as a cathode ray tube.

FIG. 5 shows the operation of the oscillation circuit 1 when the display memory 4 is time-division controlled. The control signal 13 output from the sync signal input circuit is a horizontal sync signal detection pulse, and the oscillation circuit stops only for a short period of time during this period (B), and otherwise oscillates constantly (A). The memory 4 can be written and read.

Here, the reason why the oscillation circuit 1 is stopped by the horizontal synchronization signal detection pulse is that the display character output is output in synchronization with an external video signal, so that the oscillation circuit 1 accurately performs phase alignment with respect to the synchronization signal. This is because it is necessary to do it.

[Problems to be solved by the invention]

In a conventional screen display device in which the reading and writing of the display RAM are operated by time division control, the oscillation circuit oscillates at all times except for a short period by the horizontal sync detection pulse in preparation for the arrival of control data. Since the oscillator circuit must be oscillating even when the display device is in the display-off state, the harmonic component of the oscillation frequency of the oscillator circuit is radiated, and this may jump into the video signal. However, there is a problem due to so-called spurious, which adversely affects the video signal.

The present invention has been made to solve the above problems, and an object thereof is to obtain a screen display device capable of reducing spurious due to an oscillation circuit and reducing power consumption.

[Means for solving problems]

The screen display device according to the present invention makes the oscillation circuit oscillate only when displaying characters and when inputting display control data from a microcomputer or the like.

[Action]

In the present invention, the oscillation stop control circuit for stopping the oscillation of the oscillation circuit is provided except when it is necessary, that is, when displaying characters and when the display control data is input from the microcomputer. Spurious can be reduced and power consumption can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a screen display device according to an embodiment of the present invention, in which the same reference numerals as those in FIG. 4 denote the same parts. Reference numeral 9 denotes an oscillation stop control circuit, which is added in this embodiment. The oscillation stop control circuit 9 outputs a command writing pulse 11 that is a control data transmission period from the microcomputer output from the input control circuit 3 and a display pulse 12 that indicates that a display period is output from the display control circuit 8. The horizontal sync signal detection pulse 13 output from the sync signal input circuit 6 is used as an input signal.

FIG. 2 shows a specific circuit of the oscillation stop control circuit 9. In the figure, reference numeral 21 denotes a 2-input NOR gate, which receives the command write pulse 11 and the display pulse 12 described above. 22 is 2
This is an input OR gate, and the output of the 2-input NOR gate 21 is connected to one input and the other input is connected to the sync signal detection pulse 13. Output of 2-input OR gate 22 is "H"
At this time, the oscillation circuit 1 stops oscillation.

FIG. 3 shows the oscillation state of the oscillation circuit 1.
As is apparent from the figure, the oscillation circuit 1 can be in the oscillating state (A) only at two times when the screen display device is in the display period or when the control data from the microcomputer or the like is being input. Yes, otherwise (B)
Can be

Here, the display memory 4 is time-division controlled as described above. However, by ensuring a sufficiently long time-division time by, for example, sufficiently increasing the pulse width of the command writing pulse, the horizontal synchronizing signal is written in the writing period. Even if the oscillation circuit stops during the period of the detection pulse and the phase of the oscillation circuit is adjusted, the control data can be written accurately.

[Advantages of the Invention] As described above, according to the screen display device of the present invention, in which the reading and writing of the display RAM are operated in a time-divisionally controlled manner, an oscillation stop control circuit is provided for display. Since the oscillation of the oscillation circuit is stopped except when the display control data is being input and the display control data is being input, the spurious emission from the oscillation circuit can be significantly reduced compared to the conventional one. It is effective as a countermeasure and also has an effect of reducing power consumption.

[Brief description of drawings]

1 is a diagram showing a screen display device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an oscillation stop control circuit of the above embodiment, and FIG. 3 is a timing diagram of the oscillation stop control circuit of FIG. FIG. 4 is a configuration diagram of a conventional screen display device, and FIG. 5 is a diagram showing an oscillation state of an oscillation circuit of the conventional screen display device. In the figure, 1 is an oscillation circuit, 2 is a timing generator, 3 is an input control circuit, 4 is a display memory, 5 is a character ROM (character memory), 6 is a sync signal input circuit, 7 is a display position detection circuit, and 8 is The display control circuit 9 is an oscillation stop control circuit.

Front page continued (72) Inventor Takashi Nakatani 4-chome, Mizuhara, Itami City, Hyogo Prefecture Mitsubishi Electric Co., Ltd. Kita Itami Works (72) Inventor Terunun Kubo 4-chome, Mizuhara, Itami City, Hyogo Prefecture Mitsubishi Electric Corporation Kita Itami Works

Claims (1)

[Claims] 1. A device for displaying characters, patterns, etc. on a screen of a display device, the oscillator circuit oscillating a signal serving as a reference for various timings in the device, and a control for controlling the device. An input control circuit for inputting and processing data, a sync signal input circuit for inputting a sync signal of a video signal, a display memory for storing the display content processed by the input control circuit to be displayed on the display device, A character memory for converting the display contents into characters or patterns to be displayed, a display position determining circuit for counting the synchronization signals to determine the display positions of the characters or patterns to be displayed, and the characters to be displayed. , A display control circuit for outputting a pattern or the like in synchronization with the video signal, and performing display by time-divisionally controlling reading and writing of the display memory. In the display device, the screen display device characterized by comprising an oscillation stop control circuit for stopping the input period and the character, the oscillator circuit except for the display period of the pattern or the like of the control data.