Digital display system

Abstract

A digital display system includes a monitor arranged to receive digital display data and synchronizing signals to develop displays on a cathode ray tube. The monitor is switched between different line structure and/or color definition modes in response to the polarity of one of the vertical or horizontal synchronizing signals trains. A circuit receives this train to provide control signals to the horizontal time base and/or a color signal code converter. The time base control signal, in accordance with its binary value, controls the frequency of the time base. The color converter, in response to the control signals, either passes color signals received in parallel over six input lines without change to the cathode ray tube drive circuits or converts color signals on four of the input lines to output signals on the six lines to the drive circuits.

We claim: 
     
       1. A digital display system including a computer display adapter for generating color signals, in parallel form and horizontal and vertical synchronizing pulses, and a display monitor for generating a raster scan display on a cathode ray tube in response to said signals and pulses, said monitor including control circuit means responsive to positive-going and negative-going vertical synchronizing pulses for providing first and second control signals respectively, and a horizontal time base generator coupled to receive said control signals for operation at first and second frequencies in response respectively to said first and second control signals whereby the line structure of the raster scan display varies in accordance with the polarity of vertical synchronizing pulses generated by said adapter. 
     
     
       2. A digital display system according to claim 1, including a plurality of lines for coupling said color signals from the adapter to the display monitor, said adapter generating said color signals selectively as first groups on all, or as second groups on some, but less than all, of said lines, with the polarity of generated vertical synchronizing pulses varying in correspondence with the groups, in which said monitor includes logic means receiving said plurality of lines, having a like plurality of output lines and having a further input line for receiving outputs from said control circuit means indicative of the polarity of received vertical synchronizing pulses, said logic means being responsive to said outputs to pass said first groups of color signals to said output lines unchanged and to encode the second groups into signals on all the output lines. 
     
     
       3. A digital display system according to claim 2 in which said logic means comprises a read only memory. 
     
     
       4. A digital display system including a display monitor coupled to receive parallel digital color signals and horizontal and vertical synchronizing pulse trains from a computer display adapter to develop a raster scan display on a cathode ray tube, comprising control circuit means in the monitor, responsive differentially to positive-going and negative-going vertical synchronizing pulse trains to generate respective control signals for switching the frequency of horizontal time base generator means and thereby altering the line structure of the display. 
     
     
       5. A digital display system according to claim 4, comprising a plurality of signal lines for carrying said parallel digital signals and logic means having inputs coupled to said lines, a further input for receiving control signals from said control circuit means and output lines corresponding to said signal lines and switchable in response to sets of parallel digital signals on all the signal lines accompanied by first control signals to direct the sets of parallel signals to the output lines unchanged and in response to sets of parallel digital signals to some, but less than all, the signal lines and accompanied by second control signals to encode the sets of parallel signals for generating corresponding sets of output signals on all the output lines. 
     
     
       6. A digital display system according to claim 4, comprising means for coupling control signals from said control circuit means to width control means in said horizontal time base generator to switch the width of said raster scan display in response to said control signals. 
     
     
       7. A digital display system according to claim 4, comprising further logic means receiving said vertical synchronizing pulses and said control signals to develop vertical synchronization pulses of fixed polarity for input to vertical time base generating means. 
     
     
       8. A digital display system according to claim 7, in which said further logic means consists of an exclusive NOR circuit. .Iadd. 
     
     
       9.  A digital display system comprising: a digital data processor operable to develop data sets of more than one video display format for display, said digital data processor further operable to generate horizontal and vertical synchronizing signals, at least one of said horizontal and vertical synchronizing signals having positive-going pulses and negative-going pulses wherein the positive-going pulses correspond to a first video display format and the negative-going pulses correspond to a second video display format, and;   a monitor, said monitor including a raster scanned cathode ray tube, said monitor further including a circuit responsive to the positive-going and the negative-going pulses to display a video display format corresponding to the positive-going pulses and the negative-going pulses..Iaddend. .Iadd.10. The digital display system of claim 9 wherein both horizontal and vertical synchronizing signals have positive-going and negative going pulses and up to four different video display formats may be displayed..Iaddend. .Iadd.11. The digital display system of claim 9 wherein the first video display format has a different scanning frequency from the second video display format..Iaddend. .Iadd.12. The digital display system of claim 11 wherein said scanning frequency is the   
     
     
        horizontal scanning frequency..Iaddend. .Iadd.13.  The digital display system of claim 11 wherein said scanning frequency is the vertical scanning frequency..Iaddend. .Iadd.14. The digital display system of claim 9 wherein a first video display format is a character generator format and a second video display format is an all-points-addressable format..Iaddend. .Iadd.15. The digital display system of claim 9 wherein each video display format has a different video signal format..Iaddend. .Iadd.16. The digital display system of claim 15 wherein a first video signal format comprises a color signal of a first format and a second video signal format comprises a color signal of a second format..Iaddend. .Iadd.17. A monitor for a display system in which a plurality of video display formats may be displayed and wherein each video display format has vertical and horizontal synchronizing signals, and wherein at least one of the horizontal and vertical synchronizing signals has positive-going and negative-going pulses the positive-going pulses corresponding to a video display of a first format and the negative-going pulses corresponding to a display format of a second video format which comprises: a raster scanned cathode ray tube and a circuit responsive to the positive-going and negative-going pulses to display formats on said cathode ray tube, said monitor further including a circuit responsive to synchronizing signal positive-going and negative-going pulses to switch said video display format to the format corresponding to the positive-going and negative-going pulses..Iaddend.