TRS-80 Model 1 Clone Blog #3

This is the timing information for a 800x600@60Hz signal taken from TinyVGA.  There are things called front porch and back porch for the horizontal scans and the vertical retrace, as well as the sync(hronising) pulses needed by the monitor.  Remember that there used to be things called Cathode Ray Tube monitors and these used a beam of electrons to excite phosphor on the back of the glass to make it glow.  This beam was "steered" by electromagnets to scan the face of the monitor, left to right and "flashing" on or off for each pixel, then turn off the beam, move down one pixel and back to the left, scan again left to right flashing as it goes, down one pixel, etc until the last row which at the right hand end the beam needs to turn off and move back to the top left to start again.  The move back to the left is controlled by the horizontal sync pulse and the back to the top is the vertical sync pulse.  These take time and this is what is shown by the timing diagrams.  Everything is measured in pixels and the pixel clock is what determines how long a pixel is.  This is known as a Raster Scan.