Chapter 2 NI2501/2503 Operation
©
National Instruments Corporation 2-7 NI 2501/2503 User Manual
Routing the external trigger from the front connector to the PXI trigger
lines gives you the capability to trigger multiple switch cards with only one
board connected to the external trigger from the measurement device.
All external trigger lines are compatible with TTL voltage levels and are
edge sensitive.
The external trigger from the front connector requires a minimum pulse
width of 500 ns. The line has a low pass filter to prevent false triggering.
The minimum pulse width from the PXI TTL triggers and PXI star trigger
is 70 ns.
Scanner Advanced
The NI25 01/2503 can generate a scanner advanced trigger to indicate
when the switch card is set up and ready to take measurements. Using the
driver software, you can configure the switch card to route the scanner
advanced (SCANADV) trigger to any PXI TTL trigger line, the PXI star
trigger, or the SCAN_ADV pin on the front connector. You can configure
the switch card to generate the SCANADV trigger when a relay has settled
(or debounced).
All SCANADV trigger lines are compatible with TTL voltage levels.
Because the NI2501/2503 has open collector drives on the PXI TTL trigger
lines, you can have multiple switch cards using the same trigger line in the
multicard SCANADV mode.
Modes
SCANADV has two modes of operation. In its default mode, the
SCANADV trigger asserts for 1 µs after the relay has debounced. You
can also configure the switch card for handshaking mode, in which the
SCANADV trigger goes high after a relay settles, and the SCANADV
trigger goes low after the external trigger input asserts. Use this
handshaking mode for multicard scanning.
Note The NI 2501/2503 ignores external triggers when it is not in a wait-for-trigger
state while scanning.