| 摘要 |
<p>PURPOSE:To allow the acceptance of a light pen indicating screen only with a CRT screen connected to a light pen by providing a light pen interruption flag set signal that is converted by the pen sense signals of two times. CONSTITUTION:An operator indicates and presses the screen of a CRT7-1 with a light pen 8 when the pen 8 is connected to a CRT7-b via a switch device 9. In such a case, the photodetector of the pen 8 senses the light on the screen of the CRT7-a. When a pen sense signal thus produced is converted into a light pen interruption flag set signal, the flag set signal is set previously so that it is converted for the fist time with pen sense signals of two times. Thus the value of an address counter that is corrected to a light pen address latch 10-b with the 1st pen sense signal is compared with the value extracted by the 2nd pen sense signal. Then the screen of the CRT7-a is decided. In other words, only the CRT screen connected to the pen 8 can be accepted as a designated screen.</p> |
