Chapter 3
Hardware Overview
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National Instruments Corporation
3-5
•
External Lock Mode—In external lock mode, the 1409 device receives
HSYNC, VSYNC, and PCLK signals from the camera and uses these
signals to acquire the video signals directly. You can also use this mode
to acquire from a line scan camera.
•
External HSYNC/VSYNC Mode—In external HSYNC/VSYNC
mode, the 1409 device receives the external HSYNC and VSYNC
from the connector and internally generates the PCLK signal. The
device’s genlock circuitry locks to the external HSYNC and VSYNC
signals. You can use this mode to acquire from VGA monitors
(640
x
480 resolution).
•
External HSYNC/VSYNC (HLOCK only) mode—In external
HSYNC/VSYNC (HLOCK only) mode, the 1409 device receives the
external HSYNC and VSYNC signals and internally generates the
PCLK signal. In this mode, the device’s genlock circuitry uses only the
HSYNC signal for locking. You can use this mode to acquire from
asynchronously-reset cameras which output a continuous HSYNC.
Note
Connect a FIELD signal to TRIG3 when the 1409 device is in external lock mode
with an interlaced camera.
Analog Front End Considerations
The analog front end of the IMAQ PCI/PXI-1409 device features a
calibrated gain circuit, programmable DC-restore circuit, and 10-bit ADC
as shown in Figure 3-2.
Figure 3-2.
IMAQ PCI/PXI-1409 Analog Front End
10-bit/8-bit Mode
The 1409 device digitizes the incoming video signal to 10 bits of resolution
at all times. In 10-bit mode, the 1409 device has four fixed, full-scale
ranges where the gain for each range is calibrated. The nominal full-scale
ranges are 0.20, 0.35, 0.70, and 1.40 V. As a result, the gain is not
continuously variable in this mode. To maintain compatibility with other
IMAQ analog devices, the 1409 device has an 8-bit mode, in which the
10-bit data from the ADC is converted to 8-bit data in the lookup table
(LUT) after gain correction and any digital filtering has occurred.
DC-restore
1 of 4
Gain
Analog
Video
10-bit
ADC
Digital Gain
Correction,
Filtering, and LUT
10- or 8-bit
