Waveform display apparatus

A waveform display apparatus comprising:

• a raster scan-type display unit having a horizontal input, a vertical input, a video signal input, a display surface having a specified number of main scanning lines, each of said main scanning lines having a specified number of picture elements, said display surface being raster scanned in accordance with said video signal input, each of said picture elements being optically displayed on the scanned display surface;
• a data memory for storing digital data to be displayed, said data memory having a specified number of addresses corresponding to a specified number of storage locations, said specified number of addresses being the same as said specified number of picture elements of one of said main scanning lines, each of said specified number of storage locations having a storage capacity corresponding to said specified number of main scanning lines of said display surface of said raster scan-type display unit, said data memory including
• a data input memory, operatively connected to receive said data to be displayed and having a specified storage capacity, for storing said data to be displayed;
• a display memory, operatively connected to said data input memory and to said first comparator and having a specified storage capacity, for receiving the data stored in said input data memory;
• transferring means, operatively connected to said data input memory and to said display memory, for transferring the contents of said data input memory to said display memory, wherein said specified storage capacity of said data input memory and said specified storage capacity of said display memory are equal;
• read out means, operatively connected to said data memory, for repeatedly reading said data memory in synchronism with the scanning of said main scanning lines of said raster scan-type display unit;
• scanning line number generating means, operatively connected to said read out means, for generating the number of the main scanning line in synchronism with the scanning of said raster scan-type display unit and for providing, as an output, the scanning line number corresponding to the number of the main scanning line being scanned;
• a first comparator having first and second data inputs operatively connected to said data memory and to said output of said scanning line number generating means, respectively, having a first data output active when said first and second data inputs coincide, and having a second data output active when said first and second data inputs of said first comparator are in a state of non-coincidence;
• delay means, having first and second inputs operatively connected to said data memory and to said read out means, respectively, for delaying the data read out of said data memory for a predetermined time corresponding to the time between two successive read outs of said data memory by said read out means;
• a second comparator, having first and second data inputs operatively connected to said delay means and to said output of said scanning line number generating means, respectively, and having an output, for comparing said output of said delay means with said output of said scanning line number generating means, said output of said second comparator being active when said first data input of said second comparator is larger than said second data input of said second comparator;
• first gate means, having a first input operatively connected to said output of said second comparator and having an output, for gating said output of said second comparator;
• a third comparator having first and second inputs operatively connected to said second output of said first comparator and said output of said first gate means, respectively, for comparing said second output of said first comparator with said output of said first gate means and for providing an active output when said first and second inputs of said third comparator are in a predetermined state;
• and
• first operating means, operatively connected to said first gate means and having first and second operating states, for controlling said gate means, said output of said second comparator disconnected from or operatively connected to said second input of said third comparator in dependence upon said first and second operating states, respectively;
• first signal combining means, having a plurality of inputs operatively connected to said first output of said first comparator and to said output of said third comparator, respectively, and having a output with a mean period, operatively connected to said video signal input of said raster scan-type display unit, for combining said first output of said first comparator and said output of said third comparator.