Data Translation MACH Series, User Manual

Page: 39 / 214

Principles of Operation
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For line-scan operations, signals LINE_IN
−
(pin 4) and
(pin 3) are provided on connector J2 to accept the horizontal (line)
sync signals directly from the video source.
For area-scan operations, the way in which the DT3152-LS board
determines the sync source depends on whether composite or
variable-scan video signals are connected to the board. For more
information, refer to the following sections.
Composite Video Signal (Area-Scan Mode Only)
For composite video signals (area-scan operations only), the sync
signal can come from one of the following sources:
• The current input channel (the channel being digitized). In this
case, the sync signal is stripped from the video signal (by the
Sync Stripper circuitry) and fed into the sync circuitry.
• One of the unused input channels. In this case, the sync signal
from the selected channel is fed directly into the sync circuitry.
For example, you could use camera 1 on channel 0 as your video
input source and camera 2 on channel 1 as your composite sync
source.
The voltage level of the analog sync signal is compared with the sync
threshold to determine when the sync is asserted. The sync period is
defined as the portion of the sync signal that falls below the sync
threshold. The sync is then used to generate the horizontal and
vertical timing for the input section of the DT3152-LS board. On the
DT3152-LS board, you can use software to specify a sync threshold of
50 mV, 75 mV, 100 mV, or 125 mV (nominal is 125 mV).