Browse Prior Art Database

Non-Invasive Light Pen Retrofit

IP.com Disclosure Number: IPCOM000100857D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Lamoureaux, WR: AUTHOR [+5]

Abstract

Adding a display buffer in the coaxial line between a control unit and "dumb" display terminal, and using electromagnetic pickup of the CRT retrace for synchronization, makes economical the retrofit of a light pen to a display terminal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Non-Invasive Light Pen Retrofit

       Adding a display buffer in the coaxial line between a
control unit and "dumb" display terminal, and using electromagnetic
pickup of the CRT retrace for synchronization, makes economical the
retrofit of a light pen to a display terminal.

      The display buffer which is added is a duplicate of the display
buffer in the terminal.

      Fig. 1 shows the display unit 1 and the light pen retrofit
control unit 2.  There are two problems which must be overcome: data
synchronization and CRT position.  All keystrokes are provided by the
control unit from a keyboard not shown in Fig. 1.  Commands over the
coaxial cable 3 are decoded to keep track of the cursor and tell when
the display buffers 4, 5 are being updated.  The external display
buffer (EDB) 5 thus holds values which are duplicate values to those
contained in the internal display buffer (IDB) 4. This solves the
first problem, data synchronization, by straightforward duplication.

      The second problem, synchronizing the light detection with a
data location (position on the CRT screen), is solved by adding an
electromagnetic pickup 6 to the light pen 7.  A very usable
electromagnetic signal, with high signal-to-noise ratio, is taken
from the deflection yoke 8 at all locations on the surface of CRT 9.
Furthermore, as in the case of an IBM 3278 display, the horizontal
and vertical retraces may be distinguishable by polarity, as shown in
the waveform 10 in Fig....