| 摘要 |
PURPOSE:To increase the drawing speed of a CPU to a video memory by inhibiting a read-modified writing operation when it is decided that a clipping area is included in an area except that where a clipping function is carried out. CONSTITUTION:A wait generation control block 10 outputs a wait signal in a write state of a CPU 2. An area designating coordinate register 8 designates an area where a clipping function is carried out. A clipping control block 9 decides whether the address of the CPU 2 written from the register 8 is included or not in the area where the clipping function is carried out and at the same time controls the writing operations of data to a video memory 3 for each bit. A wait cancel control block 11 outputs a control signal to cancel the output of the wait signal according to the deciding result of the block 9. Thus the drawing speed of the CPU 2 can be increased to the memory 3. |
