Light Pen Interface Circuit
Original Publication Date: 1988-Dec-01
Included in the Prior Art Database: 2005-Feb-15
This article describes the self-diagnostic technique in a machine, such as a CRT display station, having the capability to have a light pen attached.. As shown in the figure, a diagnostic circuit in a machine includes a selector 6 for producing a "light pen" signal. The selector 6 receives an output of AND gate 5 and a "light sense" signal from a light pen. In the case of the normal light pen operation, the light sense signal is selected by the selector 6. This light sense signal becomes high level when the light pen detects the video beam of the CRT and, in the other cases, it is kept at low level. Light pen-related circuits (not shown) in the machine recognize the light pen-pointing position on the CRT based on this signal. In the self-diagnostic mode, the output signal of the AND gate 5 is selected.