JPS63122365A - Automatic adjusting circuit for vertical screen width in crt monitor - Google Patents

Abstract

PURPOSE:To cope with a change in the software of the vertical synchronizing frequency of a using signal source by feeding a latch pulse, a reset pulse respectively to a latch circuit, a counter by a one shot multivibrator operated by a vertical synchronizing signal. CONSTITUTION:When the vertical synchronizing signal A is inputted to the one shot multivibrators 41, 42, the latch pulse C is outputted to the latch circuit 2 from an output terminal 4d in the timing of a leading edge and the counted output of a horizontal synchronizing signal B by the counter 1 is latched by the latch circuit 2. Then, the reset pulse D is outputted to the counter 1 from an output terminal 4c in the timing of the trailing edge of the vertical synchronizing signal A, the counter 1 is reset and the counting of the horizontal synchronizing signal B is started from zero again. Only when the level of the latch pulse C is changed from a low level to a high level, the latch circuit 2 fetches data and only when the counted result of the counter 1 changes, the output of the latch circuit 2 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a deflection circuit for a CRT monitor, and particularly to a vertical screen width automatic adjustment circuit thereof.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional vertical screen width adjustment circuit of a CRT monitor. is a current limiting resistor connected in series to this vertical screen width adjusting volume 9, and this current limiting resistor 12 is connected to the vertical screen width adjusting terminal 5a of the vertical deflection circuit 5.

Next, the operation will be explained.

The current value flowing there is determined by the sum of the resistance values of the current limiting resistor 12 connected to the vertical screen width adjustment terminal of the vertical deflection circuit 5 and the resistance value of the vertical screen width adjustment volume 9, and the vertical screen width is determined by the current value. It is determined. The vertical screen width is adjusted by manually adjusting the resistance value of the vertical screen width adjustment volume 9.

[Problem that the invention seeks to solve]

The vertical screen width adjustment circuit of a conventional CRT monitor is configured as described above, so when the vertical synchronization frequency of the signal source used changes, for example, when only the number of scanning lines changes while the horizontal synchronization frequency remains constant. This requires manual readjustment of the vertical double-sided width, and there is a problem in that it is impossible to respond to software changes in the vertical synchronization frequency in the signal source.

This invention was made in order to solve the above-mentioned problems, and its purpose is to provide an automatic vertical screen width adjustment device for a CRT monitor that can also be adapted to software-based changes in the vertical synchronization frequency of the signal source used. do.

[Means for solving problems]

The automatic vertical screen width adjustment device for a CRT monitor according to the present invention uses a counter and a one-shot multivibrator to count horizontal synchronization signals every time a vertical synchronization signal is input, and latches the result using a latch circuit. The output of the latch circuit is input to a logic gate, and the logic gate switches a vertical screen width adjustment resistor connected to a vertical deflection circuit.

[Effect]

The one-shot multivibrator in this invention is
By sending a latch pulse to the latch circuit at the timing of the leading edge of the vertical synchronization signal and sending a reset pulse to the counter at the timing of the trailing edge, it is possible to constantly detect changes in the vertical synchronization frequency based on the output of the latch circuit.

(Example〕 An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a counter to which horizontal and synchronizing signals from a CRT monitor are applied to its clock terminal 1a to perform counting. 2 is a latch circuit connected to this counter 1, 3 is a logic gate connected to the latch circuit 2, and each of these circuits uses an IC. In addition, 4 is two one-shot multivibrators 41.
A vertical synchronizing signal is applied to the input terminals 4a and 4b of both one-shot multivibrators 41 and 42, and the output terminal 4C of one shot multivibrator 41 is connected to the reset terminal 1b of the counter 1.
The output terminal 4d of the other one-shot multivibrator 42 is connected to the clock terminal 2a of the latch circuit 2. Further, 5 is a vertical deflection circuit, 6 to 8 are switching transistors connected to the output of the logic gate 3, and 9
- 11 are vertical screen width adjustment resistors connected to the switching transistors 6 - 8, and 12 are connection points between these vertical screen width adjustment resistors 9 - 11 and the vertical screen width adjustment terminal 5a of the vertical deflection circuit 5. Current limiting resistor arranged between 13~
15 is a pull-up resistor of the one-shot multivibrator 41.42, and 16 is a ceramic capacitor for noise countermeasures connected to the input terminals 4a, 4b of the one-shot multivibrator 41.42.

Next, the operation will be explained. FIG. 2 is a timing chart showing the time relationship of various signals. In the figure, A is a vertical synchronization signal, B is a horizontal synchronization signal, C is a seven-channel pulse,
D indicates a reset pulse. Vertical synchronization signal A is
When input to the one-shot multivibrator 41, 42, the latch circuit 2 clock pulse C is output from the output terminal 4d of the one-shot multivibrator 42 at the timing of its leading edge (rise), and the horizontal synchronization by the counter 1 at this time The count output of signal B is the latch circuit 2
latched by Next, the counter 1 reset pulse D is output from the output terminal 4C of the one-shot multivibrator 41 at the timing of the trailing edge (falling edge) of the vertical synchronizing signal A, the counter 1 is reset, and the horizontal synchronizing signal B is reset from zero again. Start counting. Here, the widths of the latch pulse C and the reset pulse D are set to be sufficiently short compared to the period of the horizontal synchronizing signal B. The latch circuit 2 is configured to capture data only when the level of the latch pulse C changes from low level to high level. Therefore, by repeating the above operation, the frequency of the horizontal synchronizing signal B and the vertical synchronizing signal The output of the latch circuit 2 changes only when the count result of the counter 1 changes in accordance with a change in the frequency of A.

The output of the latch circuit 2 is applied to the logic gate 3 and converted to the desired output, and the relationship between the horizontal synchronous frequency and vertical synchronous frequency of the switching transistors 6 to 8 at that time (
By energizing the transistors corresponding to the number of scanning lines, the corresponding one of the vertical screen width adjustment resistors 9 to 11 is energized to keep the vertical screen width constant. Note that the vertical screen width adjustment resistors 9 to 11 are adjusted in advance to achieve desired horizontal and vertical synchronization frequencies, respectively.

In the above embodiment, a discrete switching transistor is connected to the logic gate 3, but if an IC with an open collector output is used as the logic gate IC, the vertical screen width adjustment resistors 9 to 11 are connected to the logic gate 3. IC
If connected directly to the output of switch transistor 6~
8 may be deleted, and the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the latch circuit is
Since the configuration is such that a latch pulse and a reset pulse are sent to the counters, a CRT monitor can be realized that can respond to software-based changes in the vertical synchronization frequency of the signal source used.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a vertical screen width automatic adjustment circuit of a CRT monitor according to an embodiment of the present invention, FIG. 2 is a timing chart showing the operation of the circuit, and FIG. 3 is a circuit diagram of a conventional CRT monitor.
FIG. 2 is a circuit diagram showing a vertical screen width adjustment circuit of the monitor. 1 is a counter, 2 is a latch circuit, 3 is a logic gate, 41
．． 42 is a one-shot multivibrator, 5 is a vertical deflection circuit, 5a is a vertical screen width adjustment terminal, and 9 to 11 are resistors for vertical screen width adjustment. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. (2 others) Figure 2 (A) Vsync +++++-”]-(B)
Hsync -------T■■■3rd
Illustration procedure amendment (voluntary)

Claims (1)

[Claims] The vertical screen width is adjusted by determining the frequency change of the horizontal synchronization signal and vertical synchronization signal of the input signal, and adjusting the vertical screen width adjustment resistor connected to the vertical screen width adjustment terminal of the vertical deflection circuit accordingly. In the vertical screen width adjustment circuit of a CRT monitor that performs , further comprising a one-shot multivibrator that supplies a reset pulse to the counter, and a logic gate that converts the output of the latch circuit to a desired output,
The horizontal synchronization signal is counted based on the vertical synchronization signal, the counting result is latched, and the output of the logic gate based on this is used to determine the vertical screen width connected to the vertical screen width adjustment terminal of the vertical deflection circuit. A CR characterized by switching the adjustment resistor and automatically adjusting the vertical screen width.
T monitor vertical screen width automatic adjustment circuit.