JPS6281176A - synchronous 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 the Invention The present invention relates to a synchronization control circuit that controls a CRT controller using a synchronization signal separated from a composite video signal of an input signal supplied from a television set, video playback device, etc. It is something.

2. Description of the Related Art In a conventional synchronous control circuit, as shown in FIG.
[Video Display Processor System Design Handbook, edited by Japan Texas Instruments Co., Ltd., p. 70].

However, if the video playback device is in a special playback state and is supplied from a video playback device such as a video tape recorder, the horizontal synchronization signal and equivalent pulse are not included in the vertical synchronization period of the composite video signal that becomes the input signal. Also, since the number of horizontal pulses per field is not constant,
In order to obtain stable synchronization, it is necessary to take countermeasures when the horizontal synchronization signal and equivalent pulses are not included in the vertical synchronization period of the input signal supplied from the video reproducing device, but this is not taken into consideration in conventional circuits.

Invention solves the problem 1. The problem with this type of conventional circuit is that the input signal is simply separated into a horizontal synchronization signal and a vertical synchronization signal. It is not possible to control the start of the frame of the CRT'':1 controller by detecting a state in which a synchronization signal and an equivalent pulse are not included.

The present invention has been made in view of the above, and an object of the present invention is to provide a synchronization control circuit that can cope with the case where a horizontal synchronization signal and an equivalent pulse are not included in the vertical synchronization period of an input signal supplied from a video playback device. The purpose is

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses a pulse loss detection circuit that detects the loss of the horizontal synchronization signal and equivalent pulse in the vertical synchronization period to detect the loss of the input signal supplied from the video playback device. When a horizontal synchronization signal and an equivalent pulse are not included in the vertical synchronization period, a control pulse is output for each field.

Function The present invention has the above-described configuration to obtain a control pulse signal controlled by the output signal of the pulse missing detection circuit.
It is possible to accurately control the start of a frame of a CRT controller even in a state where a horizontal synchronizing signal and an equivalent pulse are not included in the vertical synchronizing period of the input signal.

Embodiment FIG. 1 is a block diagram showing an embodiment of the synchronous control circuit of the present invention. In FIG. 1, 1 is a signal source, and 2 is a synchronization separation circuit. A composite video signal, which is an input signal supplied from signal source 1, is separated into a composite synchronization signal and a vertical synchronization signal by synchronization separation circuit 2. The synchronization signal is supplied to a field selection circuit 3 and a pulse loss detection circuit 4.

At this time, the output of the first monostable multivibrator 4a that can be retriggered by configuring the pulse missing detection circuit 4 with the circuit shown in FIG. Pulse width TW1
Thw(Twl(2Thw.

Similarly, the output pulse width Tw2 of the second monostaple multivibrator 4b which can be retriggered is T vw (
When set to T W 2 < 2 T vw, signal source 1
When the horizontal synchronization signal and equivalent pulse are not included in the vertical synchronization period of the input signal supplied from the video playback device used as Since there is no synchronization signal and equivalent pulse, the output of the first monostable multivibrator 4a becomes a pulse signal with a period Tvw, so the output terminal 42 of the pulse missing detection circuit 4 is rL.
J, and when the horizontal synchronization signal and equivalent pulse are included in the vertical synchronization period of the input signal supplied from the video playback device, the first monostaple multivibrator 4a
Since the output of 42 is fixed at rHJ, the output terminal 42 is at rHJ.
become. In this way, the output of the pulse missing detection circuit 4 differs depending on whether the horizontal synchronization signal and equivalent pulse are included in the vertical synchronization period of the input signal supplied from the video reproduction device used as the signal source 1.

The field selection circuit 3 is a circuit that selects whether the field of the input signal is the first field or the second field. For example, the ThW/ 2
The selection can be made by detecting the difference in the number of pulses in the period. That is, in the first field, the number of pulses of Thw/2 period is an even number, and in the second field, it is an odd number.Using this difference, in the first field where the number of pulses is an even number, The field selection circuit 3 is configured such that the output of the field selection circuit 3 is "H" (or "L"), and becomes "L" (or "H") when the second field is an odd number.

In the control circuit 6, when a horizontal synchronization signal and an equivalent pulse are included in the vertical synchronization period of the input signal supplied from the video reproduction device used as the Kugata signal source 1, only the first field control pulse signal is used for each frame. The above-mentioned field selection circuit 3 and pulse omission are capable of outputting a control pulse for each field when a horizontal synchronization signal and an equivalent pulse are not included in the vertical synchronization period of the input signal supplied from the video playback device. This is possible by using each output of the detection circuit 4.

Therefore, the field selection circuit 3 and the pulse missing detection circuit 4
Since the control circuit 6 which supplies control pulses to the CRT controller 6 is controlled by the output of the CRT controller 6, the start of the frame of the CRT controller 6 can be accurately controlled according to each state.

Effects of the Invention As described above, according to the present invention, the control pulse corresponding to the state in which the horizontal synchronization signal and the equivalent pulse are not included in the vertical synchronization period of the input signal supplied from the video playback device as the signal source. can be supplied, so it is stable and accurate (
It is possible to control the start of the frame of the CRT controller.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a synchronous control circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a pulse dropout circuit in the same circuit, and FIG. 3 is a block diagram of a conventional synchronous control circuit. 2... Synchronization separation circuit, 4... Pulse missing detection circuit, 5... Control circuit, 51...
・Output terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 3 Figure 7 B'? t.

Claims (2)

[Claims] (1) A pulse loss detection circuit is provided to detect the loss of the horizontal synchronization signal and equivalent pulse during the vertical synchronization period of the input signal supplied from the video playback device serving as the signal source. A synchronization control circuit characterized in that, if the pulse missing detection circuit does not exist, a vertical synchronization signal separated from the input signal is output as a control signal by the output of the pulse loss detection circuit. (2) Under the control of a field selection circuit that detects whether the field of the input signal is the first field or the second field, if the horizontal synchronization signal and equivalent pulse are not included in the vertical synchronization period of the input signal, each field is The synchronization system according to claim 1, wherein a control pulse is output for each frame when a horizontal synchronization signal and an equivalent pulse are included in the vertical synchronization period of the input signal. control circuit.