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Browse Prior Art Database

Direct Extraction of Cursor Location From a Display

IP.com Disclosure Number: IPCOM000047124D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Barnett, CJ: AUTHOR [+4]

Abstract

This article describes a technique for monitoring the exact row and column locations of the cursor and storing the values as it is drawn on the display. These values can be read by a microprocessor system. One application of this process is when an audio output is required from the display terminal. The design can accommodate an underscore-type cursor and a blob-type cursor, and either of these when they are flashing or steady. If the microprocessor is to provide an indication of the cursor position, then it requires a means for determining the cursor location. Due to the fast scan rate of a refresh-type display, most microprocessors cannot issue I/O read commands fast enough to extract data from the refresh data stream as it is refreshed.

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Direct Extraction of Cursor Location From a Display

This article describes a technique for monitoring the exact row and column locations of the cursor and storing the values as it is drawn on the display. These values can be read by a microprocessor system. One application of this process is when an audio output is required from the display terminal. The design can accommodate an underscore-type cursor and a blob-type cursor, and either of these when they are flashing or steady. If the microprocessor is to provide an indication of the cursor position, then it requires a means for determining the cursor location. Due to the fast scan rate of a refresh-type display, most microprocessors cannot issue I/O read commands fast enough to extract data from the refresh data stream as it is refreshed. Example of scan rate Typical scan time per line for a 80-character-wide display = 50 msec approx. Therefore, scan time per character = 625 nsec = 'addr valid' time per character in refresh buffer. In the proposed solution circuitry synchronized with the scan rate of the display, but under control of the microprocessor, interfaces between the display and the microprocessor. The drawing shows the general data flow of the technique. Three counters are used in the interface. Except when data is being read by the microprocessor, they count in synchronism with the refresh data on the display. 1. The character counter counts up once for each character position on the screen. The counter is reset during each horizontal retrace. 2. A scan line counter counts the number of scan lines for each displayed row on the display. It is reset before the start of e...