| 摘要 |
A video system is disclosed which is capable of receiving digital data from a source such as a video camera, and subsequently transferring the received data into a main frame buffer for display on a video display, where the data from the source can overlay a primary image stored in the main frame buffer. An auxiliary frame buffer, consisting of a bank of dual-port RAMs, receives the data of the overlay image via its serial port and transfers this data into the randomly accessible array therein. A direct-memory-access (DMA) operation performs the transfer from the auxiliary frame buffer into the main frame buffer, with the source and destination positions in the auxiliary and main frame buffers, respectively, independently selectable. The performance of the DMA operation can be enhanced by simultaneously performing a page mode read of the auxiliary frame buffer with a page mode write to the main frame buffer.
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