| 摘要 |
PURPOSE:To prevent the break of a liquid crystal display panel due to an abnor mal input signal by detecting the abnormality of a vertical synchronizing signal inputted from the outside to perform switching to an internal vertical synchroniz ing signal generating means. CONSTITUTION:Input terminals 2 to 6 to which a video signal and horizontal and vertical synchronizing signals are inputted independently of one another are provided, and an HD presence/absence detecting circuit 22 detects the presence or the absence of a horizontal synchronizing signal HD, and a VD abnormal input detecting circuit 24 detects the abnormal input of a vertical synchronizing signal VD. Consequently, a control circuit 26 outputs a VD switching signal for selection of the signal of an internal VD oscillating circuit 28 to a VD switching circuit 27 if a horizontal synchronizing signal regarded as abnormal is inputted to the vertical synchronizing signal terminal 6. That is, a terminal a-c of the VD switching circuit 27 is turned on to input the vertical synchronizing signal VD to a clock generator 30 when the normal vertical synchronizing signal VD is inputted, putted, but a terminal b-c of the VD switching circuit 27 is turned on to input a signal INTVD outputted from an internal VD oscillating circuit 28 to the clock generator 30 when an abnormal signal is inputted.
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