Routing Considerations for E Series and S Series Devices

  • PFI 0—When exporting a signal through task-based routing to most PFI terminals, the route is reserved and committed with the task. When the task goes back to a verified state, software resources for the route are released, but the route remains in place in hardware. It remains in place to prevent glitching on the PFI terminal and to prevent any unexpected effects on external circuitry monitoring the signal. However, PFI 0 is an exception to this rule. Because PFI 0 can accept both analog and digital signals, it tristates when the task is not in the committed or running state. This behavior is intended to prevent accidental connections of an analog signal directly to digital circuitry that could damage the device.
    Note PFI 0 accepts only digital signals on the NI 6154.
    When in use, the analog trigger circuitry takes over the PFI 0 terminal internal to the device. Because of this, you cannot use PFI 0 to route any digital signals when using the analog trigger, regardless of whether you are triggering off of PFI 0 or an analog input channel. If you try to use PFI 0 for digital signals and the analog trigger at the same time, you receive a routing error.
  • Counters— The counters on these devices are very versatile and in many cases can route signals across subsystems. They can also be used to route signals to/from the I/O connector. However, when a counter is used as part of a route, you may not be able to use the counter for other applications while the route remains reserved. Most routes do not require an internal counter terminal, but many advanced routes do. For example, if you want to use the signal present at PFI 4 on Dev1 as the Start Trigger for an acquisition on Dev2, you simply need to specify /Dev1/PFI4 as the source of the trigger. However, to make the route, the signal is internally routed from /Dev1/PFI4 to /Dev1/Ctr0Source to a RTSI bus line or PXI_Trig to Dev2/ai/StartTrigger. These terminals need not be explicitly specified when programming the route. In this case, it is not obvious that a counter terminal is used to make the route. Subsequent attempts at using the counter while it is in use result in a routing reservation error. To see if the route you are making uses counter resources, consult the table displayed under the Device Routes tab in MAX.