COMPUTER VIDEO GRAPHIC SYSTEM

摘要

PURPOSE: To provide a video system having plural programmable operation modes and a refresh buffer. CONSTITUTION: A pack level detecting circuit 202 recognize a time when the pack level of a first-in first-out buffer(FIFO) 201 reaches a previously fixed level being specifiedly 3, 5 or 6 double words or the level more than that. A central processing unit can write new video data in a video memory 113 by a processor access circuit. Whenever the present pack level is equal to below a min. pack level which is set by a pack level selecting circuit 205, the processing unit access circuit is in a disenable state. The central processing unit performs access to the video memory 113 only when min. level data exists in FIFO 201, and the min. level data is selected in accordance with a present operation mode.