Abstract: A data display apparatus employs a raster scan cathode ray tube (1), a character refresh buffer (2) and three character row buffers (5,6,15) to address a character generator (3) in conjunction with a slice counter (4) or offset slice counter (18) under control of an events control module (20). This enables data within a partition on the CRT to be scrolled smoothly (scan-line-by-scan-line) and characters of different height (requiring different numbers of scans) to be displayed on the same row of the CRT.

Abstract: A programmable timing circuit for a cathode ray tube includes a register stack (48) in which events to be timed are stored so that they are presented to comparators (45, 46 or 47) in the sequence in which they will occur. Each event is coded in terms of the position (character, line or row) on the screen at which it is to occur and flags stored with the values are decoded to identify the event being timed when a match is found between the presented value and the count in a character, line or row counter (40, 41 or 42) which is indicative of the current beam position on the screen. Values in the register stack can also control internal operations of the timing circuit, for example re-setting counters or re-addressing the stack.

Abstract: A color cathode ray tube display apparatus is provided with compensation for errors due to interfering magnetic fields in which a deflection yoke causes the electron beams to raster scan across the tube, a convergence assembly on the neck of the cathode ray tube adjusting the beam convergence. Errors in the waveforms suppied to the radial convergence assembly are caused by high frequency magnetic field coupling between the yoke and the convergence assembly via the internal magnetic structure 7 of the cathode ray tube. A compensating coil 11, placed adjacent the convergence coil unit 12, 16 supplies compensating current through resistor 20 to the amplifier 15 driving the convergence coil unit, thus avoiding a fringe on the left-hand side of the screen. Alternatively, compensating current can be derived from the line flyback pulse or the logic signal initiating line flyback.