![background image](http://html.mh-extra.com/html/national-instruments-corporation/imaq-pci-1408/imaq-pci-1408_getting-started_710256035.webp)
Chapter 3
Hardware Overview
PCI/PXI-1408 and NI-IMAQ for Win95/NT
3-8
©
National Instruments Corporation
•
Field—For an interlaced video signal, a field is half the number of
horizontal lines needed to represent a frame, as shown in
Figure 3-3. The first field of a frame contains all the odd-numbered
lines. The second field contains all of the even-numbered lines.
Figure 3-3. Video Field
•
Frame—A frame is a complete image. In interlaced formats, a
frame is composed of two fields.
Programming Video Parameters
You can program all of these video parameters on the 1408 device:
•
Programmable pixel and line count—When generating an internal
PCLK, the 1408 device uses a programmable clock generator with
an advanced VCO circuit. This circuitry generates a PCLK
frequency from 11 to 16.5 MHz, depending on the horizontal count.
The standard sampling rate for RS-170/NTSC video signals is
12.3 MHz, and the standard sampling rate for CCIR/PAL is
14.75 MHz. To correct for external pixel aspect ratio errors of up
to ±9%, the VCO covers the range from approximately 11.0 to
16.5 MHz.
The 1408 device also includes a programmable line count, which
you use to switch between RS-170/NTSC (525 lines) and
CCIR/PAL (625 lines). In addition, the 1408 device supports any
line count up to 1,024 lines for nonstandard video inputs.
Note:
You can have up to 2,048 lines in interlaced mode by combining fields.
Vertical Sync
Line Region
Horizontal
Sync
Video
Line