LIGHTPEN CONTROL CIRCUIT

A control circuit for a lightpen of a random scanning computer graphics sem (10) enabling the detection of lightpen interrupts or hits on contiguous vectors having drawing periods shorter than the response time of the lightpen (13). The lightpen interrupts are temporarily held in a peripheral circuit (31,32,34,36) and are selectively released to the computer system (via 29,21) at the end of its INTERPRET phase, i.e., at the end of a period during which the display processor decides how to handle the next display instruction. The present arrangement, which prevents the arrival of the lightpen interrupt signal during the INTERPRET phase, achieves a computer graphics system exhibiting maximum use of the information furnished by lightpen hits.