| 摘要 |
A system is disclosed for generating a circle on a television raster display utilizing digital techniques. An x coordinate counter, a y coordinate counter, a radius number, and a radius + delta number, in parallel to each other, are connected to the input terminals of a multiplex switch. The multiplex switch selectively provides an output signal of the above number generators to a programmable read only memory (PROM). The memory in turn sequentially provides an output signal representing the square of the input number, i.e., x2, y2, r2 and (r + delta )2. The numbers x2 and y2 are added by an adder and the number x2 + y2 is compared by a first comparator, with the number r2 and an output is provided if x2 + y2 >/= r2. The numbers x2 + y2 is also compared by a second comparator, with the number (r+ delta ) 2 and an output signal is provided if x2 + y2 < (r+ delta )2. An output signal is provided to a television display whenever the above equations are true. Thus, each point on a television raster display is tested and a video signal is provided when the equations are both true. |
