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                                      CHAPTER 58
                        VIDEO DIGITIZER CLOCK INTERFACE (VDCI)
                          Video Digitizer Clock Interface
          INTRODUCTION
               The VDCI is a single-width CAMAC module.  It is used in 
               conjunction with a transient waveform digitizer (TWD) such
               as the Transiac model 2008 to digitize video (RS-170) 
               information.  The purpose of this module is to limit
               unnecessary handling of useless information in the digitizer
               by selecting a critical part of the picture for digitizing.
               The module does this by producing bursts of clock pulses 
               which instruct the waveform digitizer when to sample. The
               horizontal and vertical start,stop, and resolution are settable 
               and readable through CAMAC.
           DESCRIPTION
               The vertical start and stop coordinates are loaded in counters
               from their respective latches during the video's vertical sync
               pulse.  The vertical start counter counts lines until the designated
               region is reached, then enables the digitizer's clock.  The stop
               counter continues to count until it drops out of the designated 
               region, thus disabling the clock.
               The horizontal counters are loaded in the same manner as the 
               vertical except that they begin from the horizontal sync pulse.
               The start counter counts clock pulses until the designated region
               is reached, then enables the digitizer's clock.  The horizontal 
               stop counter coutinues until out of the region on that line, at 
               which point it disables the clock.  Vertical coordinates are set 
               from 0-255 and horizontal coordinates are 0-511.  The stop 
               coordinates must be larger than the start in both the vertical
               and horizontal directions.
               The vertical and horizontal resolution counters continuously
               reload themselves from their respective latches at the end of 
               each count sequence.  The vertical resolution is gated with 
               the designated region, then with the horizontal resolution 
               which has been gated with the pixel clock.  The culmination 
               of all this determines the digitizer's clock.
           SPECIFICATIONS



        VIDEO DIGITIZER CLOCK INTERFACE (VDCI)                       Page 58-2

              Inputs:
              o  Video In  -- Video signal from camera terminated in 75 Ohms.
              o  Beam Trig -- Beam related negative edge trigger NIM signal
                              terminated in 50 Ohms.
              Outputs:
              o  Video Sum -- The digitizer clock is summed with the video
                              with the video signal then run into a TV monitor
                              to give a "highlighted" visual representation
                              of the area being digitized.
              o  Video Out -- The video signal is buffered through a current
                              amplifier which feeds the digitizer's input signal.
              o  Stop Trig -- When an F25*A0 is issued to the module, it waits
                              for a beam trigger and a vertical sync, then sends
                              a positive edge trigger TTL pulse to the digitizer.
                              This triggers the digitizer and insures that the
                              memory contains that last beam pulse.
              o  Dig. Clk  -- Positive edge trigger TTL clock tells the digitizer
                              when to sample the input signal.  50 Ohm driver.
           CAMAC COMMANDS
              o  F0 A0:  Read horizontal start coordinate (R1-R9)
              o  F0 A1:  Read horizontal stop coordinate  (R1-R9)
              o  F0 A2:  Read vertical start coordinate   (R1-R8)
              o  F0 A3:  Read vertical stop coordinate    (R1-R8)
              o  F0 A4:  Read horizontal resolution       (R1-R4)
              o  F0 A5:  Read vertical resolution         (R1-R4)
              o  F16 A0: Write horizontal start coordinate (R1-R9)
              o  F16 A1: Write horizontal stop coordinate  (R1-R9)
              o  F16 A2: Write vertical start coordinate   (R1-R8)
              o  F16 A3: Write vertical stop coordinate    (R1-R8)
              o  F16 A4: Write horizontal resolution       (R1-R4)
              o  F16 A5: Write vertical resolution         (R1-R4)
              o  F25 A0: Starts the stop trigger process.
              DRAWING PACKAGE NUMBER
               233-903
              RESPONSIBLE ENGINEER
              D. G. Brown