National Instruments VXI-MXI-Express Series User Manual page 63

Using the Trigger Ports on the
NI VXI-8360LT
Driven Mode Operation
Wired-OR Mode Operation
© National Instruments
The NI VXI-8360LT allows you to extend the 8 TTL backplane triggers
over a wired VXI backplane trigger bus through convenient front panel
connectors. The wired VXI backplane trigger bus allows a simple way to
have an event in one system trigger events in other VXI systems.
The wired trigger bus physical interface is based off of the TIA/EIA-899
Multi-Point Low Voltage Differential Signaling (M-LVDS) standard. The
physical interface allows the construction of large multi-drop systems and
reliable triggering over long distance. Topologies up to 6 devices over 20 m
of cable are supported. The wired VXI backplane trigger bus may be
capable of supporting more devices over greater cable lengths but, these
configurations have not been validated by National Instruments.
The 8 triggers on the wired VXI backplane trigger bus correspond to the
8 TTL triggers on the VXI backplane (e.g., TTLTRG0* on the VXI
backplane corresponds to Trigger Number 0 on the wired VXI backplane
trigger bus). Each of the 8 physical trigger channels are independently
configurable and can be used in one of two topologies: point-to-multipoint
or multipoint-to-multipoint.
This is a point-to-multipoint configuration where one device on the trigger
channel is configured as a driver and the remaining devices are configured
as listeners. The device configured as the driver sets the state of the trigger
channel and the other devices receive that state. If two or more devices are
configured to drive the trigger channel the behavior of the bus is undefined.
This is a multipoint-to-multipoint topology where multiple devices can
assert a trigger channel to multiple listeners. For this topology, the trigger
channel behaves in a wired-OR manner with all drivers tri-stated. A bias
device is used to pull the trigger to a known, unasserted state and then the
triggering device(s) drive(s) the bus to its asserted state.
D-1 VXI-MXI-Express Series User Manual