On-screen display device for a multimode monitor and method thereof

An on-screen display device for controlling a dot clock and for a multimode monitor having a screen and responsive to a change of frequencies or polarities of synchronizing signals in received video picture signals and adapted for displaying the video picture signals and characters corresponding to signals representing said frequencies and corresponding to input picture control signals generated by an associated key pad, said device comprising:

• a microprocessor responsive to the signals from the key pad and to said synchronizing signals for providing digital display signals corresponding to said synchronizing signals and digital signals corresponding to the picture control signals;
• a digital-to-analog converter for converting the digital signals for picture control provided by said microprocessor into analog voltage signals, and generating an oscillating frequency signal in response to said digital display signals for controlling said dot clock so as to adjust the position and size of characters displayed on said screen;
• an on-screen display means for receiving said synchronizing signals and for receiving said digital signals from the microprocessor and said oscillation frequency signal from said digital-to-analog converter and generating signals for controlling the display of the synchronizing frequencies and the picture control on the screen as on-screen display characters;
• a blanking means for producing a blanking signal for blanking the display of the video picture signals on a portion of the screen corresponding to the position of the characters;
• mixing means for mixing the video picture signals and character signals supplied from said on-screen display means, said mixing means including pairs of emitter coupled transistors respectively receiving the video picture and characters and applying the same to the monitor;
• and
• a polarity detector for detecting the polarities of horizontal and vertical synchronizing signals of the video picture signals, said detector being coupled to said microprocessor and supplying polarity signals to said microprocessor for activating registers therein.