Browse Prior Art Database

DEC 338 LIGHT PEN SENSE INDICATOR

IP.com Disclosure Number: IPCOM000128420D
Original Publication Date: 1966-Nov-01
Included in the Prior Art Database: 2005-Sep-15
Document File: 4 page(s) / 18K

Publishing Venue

Software Patent Institute

Related People

Lundstrom, Stephen F.: AUTHOR [+3]

Abstract

This memorandum describes the characteristics and possible uses of the light-pen sense indicator that has been added to the Concomp Project's DEC 338 Display. The circuit involved, including the wire list used to implement this additional 338 feature, is also given.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 39% of the total text.

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THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.

DEC 338 LIGHT PEN SENSE INDICATOR

THE UNIVERSITY OF MICHIGAN, Memorandum

Stephen F. Lundstrom
CONCOMP: Research in Conversational Use of Computers
F. H. Westervelt, Director, ORA Project 07449 supported by: DEPARTMENT OF DEFENSE, ADVANCED RESEARCH PROJECTS AGENCY, WASHINGTON, D. C.

CONTRACT NO DA-49-083 OSA-3050, ARPA ORDER NO 716 administered through: OFFICE OF RESEARCH ADMINISTRATION ANN ARBOR, November 1966

ABSTRACT

This memorandum describes the characteristics and possible uses of the light-pen sense indicator that has been added to the Concomp Project's DEC 338 Display. The circuit involved, including the wire list used to implement this additional 338 feature, is also given.

I. GENERAL DISCUSSION

The addition of the light pen sense indicator (LPSI) to the 338 Display allows the 338 Display Control to sense the past history of the light pen. The impulse for this addition came from programming considerations of some types of display program sequences A later section describes some of the potential utility of this feature. In general, one may notice that there are many instances in display programming when the light pen is to be used to point generally at something (perhaps at a light button) rather than to indicate precise display coordinates. In many cases, the only reason for pointing is to move into another portion of the display file. Previously, this requirement was satisfied by PDP-8 central processing unit (CPU) interaction. With the addition of the LPSI, the display program itself may satisfy these requirements without CPU interaction.

II. LIGHT PEN SENSE INDICATOR (LPSI) DESCRIPTION

The light pen sense indicator is set on any light pen hit at any time; it may not be disabled. The 338 Display Control may) under program control clear the LPSI and/or cause a display program skip if the LPSI is not set.

The programmer accomplishes the above tasks by microprogramming the remaining two bits of the control state instruction 62XX as follows:

(Image Omitted)

During the execution of the above instruction the microprogrammed bits Y and Z have the following meanings:

Y = 0 Do not clear the LPSI.

University of Michigan Page 1 Nov 01, 1966

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DEC 338 LIGHT PEN SENSE INDICATOR

Y = 1 Clear the LPSI.

Z = 0 Do not skip on LPSI test.

Z = 1 Do a display file skip (2 locations) if the LPSI is not set.

III. POTENTIAL USES

This section will describe briefly two possible uses of the new LPSI. No attempt has been made to be exhaustive, only suggestive.

A. Light Pen Tracking

One of the major problems in light pen tracking is in moving the tracking cross fast enough when the operator is (moving the light pen at high speeds. The following high speed tracking algorithm is an extension of one successfully implemented by the author.
1. Clear the LPSI and enable the light pen.
2. Draw the normal tracking cross. Any light pen hits during this time are treated in the same manner...