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Browse Prior Art Database

Locate Light Pen Position

IP.com Disclosure Number: IPCOM000093171D
Original Publication Date: 1967-Jun-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Floros, TG: AUTHOR [+2]

Abstract

Location of a light pen on a blank area of a CRT display is automatically determined without resort to CPU interrupts. Special orders in the display buffer permit character flooding of the display if a position detection does not occur during frame regeneration.

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Locate Light Pen Position

Location of a light pen on a blank area of a CRT display is automatically determined without resort to CPU interrupts. Special orders in the display buffer permit character flooding of the display if a position detection does not occur during frame regeneration.

Light pen 10 detects the presence of light on the surface of CRT display 11. Actuation of switch 12 indicates that the position of 10 relative to 11 is to be determined. Actuation of 12 sets latch 15 which causes single-shot 16 to generate a pulse to set synchronization latch 18 thus assuring position detection despite contact bounce of 12. Buffer 20 is a memory containing a sequence of orders or instructions which are regenerated for producing each frame presented on 11. The beginning of a regeneration cycle of 20 with the start order causes And 21 to be conditioned which, if 18 is set, sets latch 22 to condition And 23. Light detected by 10 and amplified by 24 completes the conditioning of 23. The latter produces an output at 25 for gating the content of the X-Y registers thus indicating the position of 10. Actuation of 12 after the start order is passed in a given cycle results in no output until the start order is reached at the beginning of the next cycle.

An output at 25 after the start order of a cycle of 20, but before reaching the no-detect transfer NDT order, results in a branch and the NDT order is not reached. Conversely, if no output at 25 results before NDT is reach...