JP2516941B2 - Screen display controller - Google Patents

Description

TECHNICAL FIELD The present invention relates to a screen display control device for displaying characters and patterns on a display device such as a cathode ray tube.

[Conventional technology]

FIG. 7 shows a general example of screen display. This is an example of a screen display in a device that displays characters and patterns on a television (hereinafter referred to as "TV") screen or the like.

A block system diagram of a conventional screen display control device is shown in FIG. In FIG. 3, 1 is an oscillation circuit that outputs an oscillation output signal OSC, RO and CO are external resistors and capacitors that determine the oscillation frequency, 30 is an image display control device main body, and the image display control device is shown. In the main body 30, 2 is a timing generator that inputs the oscillation output signal OSC output from the oscillation circuit 1 to generate various timings, 3 is a display memory, 4 is a character ROM, 5 is an output circuit, and 6 is a horizontal synchronization signal. A horizontal sync signal counter that counts h to determine the display position on the screen, and 7 is an input signal of the output signal of the timing generator 2, the output signal of the horizontal sync signal counter 6 and the vertical sync signal v. RO
M4, a display control circuit for controlling the output circuit 5, 8 is an input data control circuit for controlling various input data and storing display contents in the display memory 3, 21 is an integrating circuit composed of the resistor Ro and the capacitor Co, T1 is an input terminal of the integrating circuit 21,
T2 is an output terminal.

As shown in FIG. 7, the horizontal size of characters and patterns displayed on the TV screen is determined by the oscillation frequency of the oscillation circuit 1. Further, at the time of display on the screen, the display memory 3 reads data from the character ROM 4, the data is output from the output circuit 5 to a TV or the like, and characters or patterns are displayed on the TV screen.

In the screen display control device as described above, since the oscillation frequency of the oscillation circuit 1 and its phase are completely asynchronous with the TV side, in order to display characters or patterns on a cathode ray tube or the like, the oscillation circuit using the horizontal synchronization signal h is used. Phase 1 must be performed.

A detailed configuration of the oscillator circuit 1 is shown in FIG. 4 for explaining the phase matching. In FIG. 4, the oscillator circuit 1 is
Inverter 11,13,15, 2-input NAND gate 12 and resistance value
It is composed of resistors 10 and 14 of R _s and R _f . The input side of the inverter 11 and the output side of the 2-input NAND gate 12 are connected via a resistor 14. This connection and the resistor 10 form a Schmitt type oscillation circuit. By inputting the horizontal synchronization signal h to the inverter 15 in the oscillation circuit 1, the oscillation of the oscillation circuit is completely stopped during the pulse generation period of the horizontal synchronization signal h, and the oscillation is started after the pulse of the horizontal synchronization signal h disappears. Phase matching is performed by the method of causing.

Timings of signals in FIG. 4 are shown in a time chart of FIG. 5 (a) shows the signal waveform of the T1 terminal to which the inverted signal ▲ ▼ of the oscillation output signal OSC is connected via the resistor RO, and FIG. 5 (b) shows the inverter of the oscillation circuit 1.
The horizontal synchronizing signal h input to 15 is shown.

[Problems to be solved by the invention]

The conventional screen display control device is configured as described above, and since the oscillation circuit stops oscillation during the pulse width of the horizontal synchronizing signal h, the interaction between the input data control circuit 8 and the display memory 3 is controlled during this period. There is a drawback that you cannot do it.

Therefore, when the pulse width of the horizontal synchronizing signal h is shortened as shown in FIG. 6 in order to eliminate this drawback, the oscillation output signal
Inverted signal ▲ ▼ of OSC is connected via resistor RO T
Since the pulse of the horizontal synchronizing signal h disappears and oscillation starts before the 1 terminal is lowered to the ground potential, the oscillation timing is T1.
Depending on the potential of the terminal, accurate phase matching cannot be performed, and thus there is a problem in that characters and patterns to be displayed are blurred.

The present invention has been made in view of such a point,
The purpose of this is to prevent the oscillation circuit from stopping even if the pulse width of the horizontal sync signal is positively shortened, to enable correct phase alignment, and to shorten the oscillation stop period to prevent oscillation. (EN) Provided is a screen display control device which makes a circuit close to continuous oscillation, thereby extending a period in which the exchange of image information between a display memory and an input data control circuit can be controlled and extending a writable and readable period in the display memory. Especially.

[Means for solving problems]

In order to achieve such an object, in the screen display control device according to the present invention, the drain is connected to the input side of the resistor 10, the gate is connected to the horizontal synchronizing signal h or its inverted signal, and the source is connected to the ground or the power supply. The field effect transistor is provided in the oscillation circuit 1.

[Action]

In the present invention, the field effect transistor ensures that the potential of the T1 terminal to which the inverted signal ▲ ▼ of the oscillation output signal OSC is connected via the resistor RO in response to the pulse of the horizontal synchronizing signal h is set to the ground potential or the power supply potential. Since it is fixed, the pulse width of the horizontal sync signal can be shortened without impairing the oscillation phase adjustment accuracy, and the horizontal sync signal can control the exchange of image information with the display memory to extend the period for writing and reading in the display memory. The possible period can be extended.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an oscillation circuit 1 which constitutes a screen display control device according to the present invention. In FIG. 1, 20 is a Schmitt circuit for inverting output having a reset input, 21 is an integrating circuit, and 22 is an N-channel field effect transistor. Further, in FIG. 1, the same or corresponding parts as those in FIG. 4 are designated by the same reference numerals.

Next, regarding the operation of the apparatus configured as described above,
This will be described with reference to FIGS. As shown in FIG. 2 (a), since the oscillation circuit 1 is a Schmitt circuit whose oscillation frequency is determined by the Rf / Rs ratio, the “H” threshold level V _THH between the power supply potential V _DD and the ground potential V _{SS is} Oscillation occurs between the "L" threshold level V _THL by charge / discharge determined by the external resistor RO and the external capacitor CO. However, when a pulse of the horizontal synchronizing signal h occurs, the oscillation output signal OSC is generated by the N-channel field effect transistor 22. The T1 terminal to which the inversion signal ▲ ▼ of is connected via the resistance RO drops to the ground potential V _SS and oscillation is stopped. When this pulse disappears, oscillation starts, but the inverted signal ▲ ▼ of the oscillation output signal OCS and the T1 terminal always start rising from the ground potential V _SS, so the oscillation timing is constant and accurate phase adjustment is possible. Becomes

It should be noted that the horizontal synchronizing signal h and the two-input NA in the above embodiment are used.
The ND gate 12 and the N-channel field effect transistor 22 whose source is grounded are respectively inverted signals of the horizontal synchronization signal,
The input NOR gate and source may be replaced with a P-channel field effect transistor connected to the power supply, and the same effect as that of the above-described embodiment is obtained.

〔The invention's effect〕

As described above, according to the screen display control device of the present invention, the oscillation output signal is generated by the pulse of the horizontal synchronizing signal h.
Inverted signal ▲ ▼ of OSC is connected via resistor RO T
Since the field effect transistor 22 for fixing the potential of 1 to the ground potential V _SS or the power supply potential V _DD is provided in the oscillation circuit 1, it is possible to perform accurate phase alignment with a horizontal synchronizing signal having a short pulse width. There is an effect that blurring does not occur in the characters and patterns to be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an oscillator circuit constituting a screen display control device according to the present invention, FIG. 2 is a time chart diagram for explaining the operation of the circuit of FIG. 1, and FIG. FIG. 4 is a block diagram of a conventional screen display device, FIG. 4 is a circuit diagram showing an oscillation circuit which constitutes the conventional screen display device, and FIGS. 5 and 6 are time charts for explaining the operation of the circuit of FIG. FIG. 7 is a diagram showing a screen display example in a device for displaying characters and patterns on a TV screen or the like. In the figure, 1 is an oscillation circuit, 2 is a timing generator, 3 is a display memory, 4 is a character ROM, 5 is an output circuit, 6 is a horizontal synchronizing signal counter, 7 is a display control circuit, and 8 is a display control circuit.
Is an input data control circuit, 20 is a Schmitt circuit, 21 is an integrating circuit, 22 is a field effect transistor, and 30 is a screen display control device body.

Front page continuation (72) Inventor Shinji Suda, 4-chome, Mizuhara, Itami-shi, Kitaitami Works, Mitsubishi Electric Corporation (72) Inventor, Kazuo Aoki 4-chome, Mizuhara, Itami-shi, Kitaitami Works, Mitsubishi Electric Corporation

Claims (1)

(57) [Claims] 1. A screen display control device main body for displaying characters or patterns on a display device such as a cathode ray tube, an inversion output Schmitt circuit having a reset input to which a horizontal synchronizing signal is input, and the Schmitt circuit input. Connected to the output of the Schmitt circuit, the output connected to the input of the Schmitt circuit, the drain connected to the input of the Schmitt circuit, the gate connected to the reset input of the Schmitt circuit, and the source connected to ground or the power supply. And an oscillating circuit for supplying an oscillating signal whose size in the horizontal direction such as a pattern displayed on the screen is determined in accordance with the frequency of the screen display device body. Screen display control device.