Direct memory access apparatus in image processing system and external storage device used therein

A direct memory access apparatus for use in an image processing system that displays an image on a raster scan monitor, said apparatus comprising:

• a data storing means for storing a data to be transferred;
• a data receiving means for receiving a transferred data;
• an address value generating means for generating a first address value and a second address value necessary for direct memory access;
• a horizontal blanking period detecting means for detecting a horizontal blanking signal which is synchronous with a horizontal blanking period of said raster scan monitor;
• a vertical blanking period detecting means for detecting a vertical blanking signal which is synchronous with a vertical blanking period of said raster scan monitor;
• a data transfer request means for generating a data transfer request signal when said horizontal blanking detecting means detects the horizontal blanking signal and said vertical blanking detecting means does not detect the vertical blanking signal;
• and
• a first data transfer means for reading, in response to said data transfer request signal from said data transfer request signal from said data transfer request means, said data to be transferred from said data storing means in accordance with said first address value, said first data transfer means transferring the read data to said data receiving means in accordance with said second address value.