JP2792323B

PURPOSE:To surely enable performing clear operation of static memory with input of a clear signal of one time by counting the number of rows of a graphic display in excess by one in a counting circuit. CONSTITUTION:When a clear signal 9 is inputted to a clear signal control circuit 4, a counter circuit A 3 starts to count by using the most significant column address signal 15 having speed of two times the least significant row address signal as a clock. And when the number of rows on a graphic fluorescent display tube 8 are counted in excess by one, a reset signal is outputted to the clear signal control circuit 4, and counting by the counting circuit A 3 is stopped by a control signal 17. During the time, blank data 11 is successively written by a row address signal 13 and a column address signal 14, and a static memory is cleared. Therefore, clear operation of the static memory 5 is performed double, clear operation can surely be realized with input of one time of the clear signal 9.