PURPOSE: To speed up the generation of a vector by operating alternate bits of one vector by two digital differential analyzers.

CONSTITUTION: A vector generating circuit consists of digital data analyzers 11, 12, an X counter 13, the 1st Y counter 14, and the 2nd Y counter 15. To write two dots in a memory during one memory cycle, two digital data analyzers for the value of X and that of (X+1) are prepared to calculate two dot positions of a Y value for a certain X value and a Y value for an (X+1) value simultaneously.