Patent GB-1506984-A (GB)
Title: Data system
IPC: G06F11/10
Filed: 1975-03-03
Abstract: 1506984 Data display systems ONTEL CORP 3 March 1975 [6 March 1974] 31223/76 Divided out of 1503381 Heading H4T A data display system includes a data memory 32 having character storage locations for storage of data characters and control characters, and a display screen (not shown) for display of characters stored in the memory, the display including a plurality of text lines each with a plurality of character positions, each text line being applied to the display screen in a text line sweep, displays being cleared from text lines of the display screen by assigning to each character position on the display screen a respective character storage location within the data memory, assigning a first control character to indicate that the balance of a text line is to be unconditionally cleared, applying the first control character to the character storage location assigned to the first character position to be cleared in each text line the balance of which is to be unconditionally cleared, applying sequentially to the display screen from the character storage locations the characters to be displayed in each text line, sensing the first control character by means of a sensor 162, and for each text line for which the first control character is sensed, clearing the display screen for the balance of that text line. The first control character may be assigned by a central processing unit 26 of a data processing system which shares the data memory 32. A second control character may be assigned to indicate that characters for the balance of a text line are to be conditionally cleared, a tagging characteristic being assigned to those data characters which are to be protected from clearing, the second control character being applied to the character storage location assigned to the first character position to be cleared in each text line to be conditionally cleared. The second control character and the tagging characteristic are sensed in respective sensors 168, 174, and for each text line for which the second control character is sensed, those data characters for which the tagging characteristic is not sensed are cleared for the balance of that text line. Clearing is accomplished by diverting the input of a switch 150 from its normal connection to the data memory 32 to a source of a "clear display" code, diversion being effected by the sensors 162, 168, 174 connected to the control input of switch 150. The tagging characteristic may be an additional data bit for each data character not to be cleared, a particular combination of data bits, the absence of a data bit, or a particular sequence of data characters to indicate that subsequent data characters are not to be cleared followed by another particular sequence of data characters to indicate that subsequent data characters are to be cleared. As new data is entered into data memory 32 to replace data displayed on the display screen, following each new data character written into memory 32 an "unconditional clear all spaces" character may be written into the next contiguous location, so that that character is displayed with the balance of the relevant text line cleared. Alternatively, a "conditional clear" character may be written into the first subsequent unprotected location, resulting in the display of the new character with the balance of the relevant text line being cleared of untagged characters.