Slow Shutter Control Signal

This option is similar to [;TS Shutter control signal] except that it offers greater flexibility and the ability to have duty cycles extending over many frames in time.

The timing singal is available on the DTR line of COM1 (normally connected to Audio channel 2 input of the VTR). This signal may be used for a variety of other timing purposes such as triggering a strobe lamp or providing markers on the audio channel of the video tape..

The timing signal is generated in the following manner:

           The incoming video signal is acquired continuously to buffer 0. The
           input look up table is set so that intensity 255 is mapped to 254.

           A single dot (intensity 255) is written to the screen at some
           poin. This point is the ON position. The position is specified by
           the user. When the incoming digitized signal overwrites this
           point, the DTR line is driven high.

           There is a delay for a pre-specified interval (based on the number
           of sync pulses) - the Time interval shutter to be open.

           A single dot (intensity 255) is written to the screen at some
           point. This point is the OFF position. The position is specified
           by the user. When the incoming digitized signal overwrites this
           point, the DTR line is driven low.

           There is a delay for a pre-specified interval (based on the number
           of sync pulses) - the Time interval shutter to be closed.

           The previous steps are repeated.

Line at which shutter to be opened ?

This entry specifies the line at which the DTR signal is to be driven high. Whether this occurs on an odd or even video field depends on the time the shutter spends open and closed. The openning and closing points can switch between even and odd fields, or remain even/odd depending on the user's requirements.

Note that if an odd line number is specified here, and the sum of the open and close shutter periods is an even number of fields, then the open will always be on an odd field. Similarly, if an even line number is specified, then the openning will be on an even field.

Time interval shutter to be open ?

This entry specifies the basic time period for which the shutter will remain open. The value entered will be rounded to an integer number of video fields. Finer control of the timing is provided by the next entry. If set to zero, then the shutter will be closed during the same video field.

Line at which shutter to be closed ?

This entry specifies the line at which the DTR signal is to be driven low. Whether this occurs on an odd or even video field depends on the time the shutter spends open and closed. The openning and closing points can switch between even and odd fields, or remain even/odd depending on the user's requirements.

Time interval shutter to be closed ?

This entry specifies the basic time period for which the shutter will remain closed. The value entered will be rounded to an integer number of video fields. Finer control of the timing is provided by adjusting the open and close lines. At least one sync signal must be detected before the shutter is opened again. As a result, the minimum time interval corresponds to one video field.

NOTE: The if the four control values are set to 31, 0, 255 and ::8, then the resulting timing signal is almost identical to that produced by [;VVA Add time code pulses].

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