Patent GB-1486219-A (GB)
Title: Cursor for use in a display
IPC: G06F17/21
Filed: 1974-11-12
Abstract: 1486219 Cathode-ray tube displays XEROX CORP 12 Nov 1974 [23 Nov 1973] 49000/74 Heading H4T A character generator 10, Fig. 1, includes at least one circuit Fig. 4, for generating cursor video signals for displaying a cursor at a predetermined position on the character display, the circuit of Fig. 4 including horizontal and vertical counters, 184, 186, the vertical counter 186 counting the overflow signals from horizontal counter 184. Horizontal and vertical position registers 182, 188 receive respective signals from a computer 12, Fig. 1, which controls the character generator 10, in response to signals from an input device 3 such as a digital pointer for positioning the cursor. The contents of horizontal position register 182 are loaded into horizontal counter 184 on the occurrence of each horizontal blanking signal and the contents of vertical position register 188 are loaded into vertical counter 186 on the occurrence of each vertical blanking signal. The horizontal counter counts clock pulses supplied via a circuit 184 until it overflows indicating that the horizontal cursor position has been reached, and vertical counter 186 is then incremented. The counters 184, and 186 proceed to function until the vertical counter 186 indicates that the vertical position of the cursor has been reached. When this happens addresses are presented to a cursor memory 190 from the vertical counter 186 and video information stored in the memory 190 is loaded into a cursor shift register 192; the loading of register 192 is enabled by a CURSOR CYCLE signal generated in response to the overflow signal from horizontal counter 184. On the next scan line, when the horizontal counter 184 overflows the cursor shift register 192 starts shifting out cursor video information. The cursor may be a rectangle, the upper left hand corner of the rectangle being displayed first. A cursor mode register 196 supplied with information from the computer supplies a signal to control the intensity of the displayed cursor; it may also supply a signal to cursor shift register 192 so that the shift register supplies valid information only when the displayed characters are caused to blink. Cursor mode register 196 may further supply control signals to vertical counter 186 and circuit 198 to double the vertical and horizontal dimensions respectively of the cursor. A character count register 200 indicates the character displayed beneath the cursor. The display device 1, Fig. 1, is associated with a keyboard and input device 3 and receives as input the output of a video mixer 14 which may provide at its output the output of character generator 10 or the output of an external video source such as a television camera 16, or an overlayed partitioned display from the outputs of the generator 10 and camera 16, as determined by the information supplied to the character generator 10. The character generator 10 may provide for the shifting of the displayed characters and for the display of characters having widths and/or heights twice the normal dimensions. The intensities of the characters may be controlled and overlayed characters may be produced. The computer 12 may provide for the use of different fonts of characters. The character generator 10 may include a first memory for storing character-representative binary information, a second memory for storing instructions and processing circuitry for producing character-representative video signals, the processing circuitry processing the odd and even bits of the signals separately and simultaneously and producing respective high and low intensity video signals which are fed to display device 1.