EXTERNAL SYNCHRONIZING CIRCUIT

摘要

PURPOSE:To use a dynamic memory as a display memory by synchronizing horizontally and vertically synchronizing signals obtained from the external through a television with display system timing generated in its inside without amplifying jitter. CONSTITUTION:A source oscillation clock 1 has an almost fixed phase relation to an external horizontally synchronizing signal 10 and an external vertically synchronizing signal 11. A clock generating circuit 2 generates a clock stop timing signal 13 showing timing generating no trouble even if a column address entering signal of a dynamic RAM, a row address entering signal and a one-picture element clock are interrupted to control the stop of the clock. A horizontal counter 3 counts up the number of picture elements in the horizontal direction, converts the counted value 6 and generates a horizontal system displaying address. A vertical counter 5 generates a vertical system display address 9. A vertical synchronization forecasting circuit 7 determines a timing enabled to stop a clock immediately before the succeeding horizontal synchronization position from the timing receiving the external horizontally synchronizing signal 10.