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Chapter 4
Signal Connections
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National Instruments Corporation
4-3
PCI/PXI-1408 and NI-IMAQ for Win95/NT
VSYNCIN±
Use VSYNCIN± when the 1408 device is in external lock mode. VSYNC is a
synchronization pulse generated at the beginning of each video frame that tells the
video monitor when to start a new field. You can set VSYNCIN in TTL or RS-422 mode
depending on jumper W3 configuration. In RS-422 mode, both and
VSYNCIN- receive the VSYNC signal. The VSYNCIN polarity is programmable.
CSYNCIN±
Use CSYNCIN± when the 1408 device is in CSYNC external mode. CSYNC is a signal
consisting of horizontal sync pulses, vertical sync pulses, and equalizing pulses only. You
can set CSYNCIN in TTL or RS-422 mode, depending on jumper W3 configuration. In
RS-422 mode, both and CSYNCIN- receive the CSYNC signal. The
CSYNCIN polarity is programmable.
CSYNCOUT
CSYNCOUT is a TTL output of the internal CSYNC signal. In CSYNC external mode,
CSYNCOUT maps directly to CSYNCIN. In standard mode, the synchronization
circuitry of the 1408 device generates CSYNCOUT.
TRIG<3..0>
Triggers <3..0> are TTL I/O lines used to start or stop an acquisition or output an
acquisition status. You can program the triggers to be rising- or falling-edge sensitive.
You can also program the triggers to be programmatically asserted or unasserted similar
in function to a digital I/O line. You can program TRIG<3..0> to reflect the following
status bits:
Status Bit
Description
AQ_IN_PROGRESS
Signals an acquisition in progress
AQ_DONE
Signals an acquisition is completed
HSYNC
The appropriate HSYNC signal
PCLK
The A/D sampling signal
GND
GND is a direct connection to digital GND on the 1408 device.
+5V
+5V is a fused connection to +5 V on the 1408 device that allows you to power external
triggering circuitry with up to 100 mA.
Table 4-1. I/O Connector Signals (Continued)
Signal Name
Description