| 摘要 |
A video display terminal permitting substantially continuous scrolling of the display. Each character row of the display is stored in the display memory in a memory segment which also stores one or more parameter bytes associated with the character row. A first parameter byte portion indicates the number of the scan line on which the display of that character row is to commence during the current frame. A second parameter byte portion indicates the number of scan lines of that character row which are to be displayed during that frame. A memory address within the parameter bytes indicates the address of the memory segment storing the next character row to be displayed. This memory address is applied directly to the DMA controller. As a consequence, scrolling only requires a CPU interrupt during each vertical retrace interval to update the parameter byte information to increment and/or decrement the first scan line number and the number of scan lines and to link the memory segments as required when a row is scrolled completely off the display and when scrolling of a new row onto the display is initiated.
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