Patent GB-1518959-A (GB)
Title: Gas discharge panel display apparatus
IPC: G06F3/038
Filed: 1975-12-15
Abstract: 1518959 Matrix displays; input devices INTERNATIONAL BUSINESS MACHINES CORP 15 Dec 1975 [3 Jan 1975] 51202/75 Headings G5C and G4H In a gas discharge display panel 12, having row 14 and column 17 orthogonal electrodes insulated from the gas, coupled to a light pen 81 viewing at most a few cells, an individual cell or groups such as a row or column can be temporarily marked for recognition by the light pen; alternating "sustain" pulse voltages are applied to all row electrodes and similar voltages but differing in phase to all column electrodes (Fig. 2, not shown) to maintain the emission of pulses of light from those cells previously activated by a "write" signal and not erased by an "erase" signal: the alternating waveforms to a row or column to be marked, or both waves to a cell to be marked are modified so that those cells previously activated by a "write" signal emit light over a part of the cycle different from that in the corresponding unmasked cells: the light pen made sensitive only over the corresponding part of the cycle by timing line 86, detects the marking. If the marking of a row is scanned from top to bottom of the panel, followed or preceded by a scan of columns from side to side, the numbers of the row and column detected by the light pen indicate the position of the pen, alternatively individual cells may be scanned across the whole panel, giving the the position of the pen in one stage. Cells are written by an undisclosed "write" waveform applied to gate 73 and passed on by a "write" signal on line 59 to transformers 28 and 39 which, activated by switching on transistors 29 and 42, are connected to those electrodes whose transistors 24-25-26 and 9-10-11 are NOT switched on. Light emission, apparently taking place on sudden deviation of the cell voltage away from mean in either direction, is maintained on "written" cells in succeeding cycles by the application of a "sustain" wave, until erased by an undisclosed "Erase" waveform in the same manner as "write". During the "sustain" period a row may be "marked' by applying a signal to "Row Disturb" line 61 energizing transformer 28 via gate 31 and transistor 29, switching on transistors 24-25- 26 on all rows except that to be marked and applying a pulse at the required time in the cycle to the "sustain" line of gate 75 of an intensity to match the "sustain" level at the secondary of transformer 28 (Fig. 2, not shown). During the pulse, transistor 33 is made to conduct and 32 not, blanking the normal "sustain" wave. A column may be similarly marked via "Column Disturb" line 62 and transformer 42 applying a pulse of opposite sign to line 37, while transistor 47 conducts and 46 blocks to blank the normal "sustain" wave (Fig. 3, not shown). To mark an individual via "Cell Disturb" line 63 pulses are applied to both its row and column as above except that the marked column transistor 9, 10, 11 is the only one conducting, and the pulse is applied via transformer 39 to make line 36 positive (Fig. 4, not shown). Time shifted light pulse emission can then occur only in the cell between the selected row and column; half selected and unselected cells remain with normal "sustain" waveform.