| 摘要 |
An interface and memory system is disclosed which receives a digital raster scan image from an external source and displays this image as an inset window on a video monitor display. The input image is asynchronous with respect to the display refresh. The pipeline dual memory system is composed of update and display buffers. If the vertical rate of the input signal is greater than the vertical rate of the display refresh, the update buffer copies its entire contents into the display buffer every time the input signal completes a frame update. If the vertical rate of the input signal is less than the vertical rate of the display refresh, the copy operation is initiated just after the start of the active portion of the input frame at a vertical position equal to the top line of the input window. A continuous display is provided because no interaction between input, copy and display refresh operations is possible.
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