Browse Prior Art Database

CRT Display Character Protection

IP.com Disclosure Number: IPCOM000087465D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 62K

Publishing Venue

IBM

Related People

Greene, WB: AUTHOR [+3]

Abstract

This system includes a host central processing unit (CPU) 1 with associated channel la, storage 2, and a device attachment 3 incorporating a microprocessor 4 for the interconnection of a cathode-ray tube (CRT) display unit 5 having a keyboard 6 and display screen 9. A device card 7 (Fig. 2) mounts various circuit chips as follows: C = Channel M = Microprocessor CRT = Cathode Ray Tube ROS = Read-Only Storage Random-Access Memory

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

CRT Display Character Protection

This system includes a host central processing unit (CPU) 1 with associated channel la, storage 2, and a device attachment 3 incorporating a microprocessor 4 for the interconnection of a cathode-ray tube (CRT) display unit 5 having a keyboard 6 and display screen 9. A device card 7 (Fig. 2) mounts various circuit chips as follows:
C = Channel
M = Microprocessor
CRT = Cathode Ray Tube
ROS = Read-Only Storage Random-Access Memory

The most important character attribute for a CRT display is that of character protection. In the past this attribute was implemented by either concatenating an extra hardware bit, independent of the character code, together with each displayable character code, i.e., EBCDIC or ASCII, or by utilizing as an attribute code the displayable character code designated just prior to the actual displayable character to be protected. In the former case, an extra hardware bit is required for each character code necessitating additional hardware cost. In the latter case, the attribute character is nondisplayable, thus unusable as a display character. Furthermore, a trailing attribute character code is required at the end of the protected character stream to actually cause the protected attribute to terminate. The trailing attribute character is nonusable for character display.

EBCDIC (8 bits) code is used for characters to be displayed in the data processing system and the bits are modified if the character is "protected", e.g. cannot be operator modified. This modification of each one-byte character code is effected by a microcode routine of the micro-processor display controller 4 utilized when the characters are transferred from the host CPU 1 to the refresh buffer 8 associated with the display. When characters are returned from the refresh buffer 8 to the CPU 1 via the microprocessor display controller 4, another routine strips the protect bit from each protected character. The technique prevents an operator from destroying or modifying character data on the CRT display from the local keyboard.

The protect attribute bit is contained within the actual 8-bit character code structure (Fig. 3), thus eliminating any requirement for extra hardware attribute bits or resorting to nondisplayable attribute characters. This technique is suitable for a 128 displayable character code set contained...