National Instruments Data Acquisition Device NI USB-621x - Manual (Page 89)

Chapter 7 PFI
NI USB-621x User Manual 7-2 ni.com
Figure 7-2 shows the circuitry of an output PFI line.
Figure 7-2. USB-621x PFI Output Circuitry
When a terminal is used as a timing input or output signal, it is called PFI x.
When a terminal is used as a static digital input or output, it is called P0.x,
P1.x, or P2.x.
The voltage input and output levels and the current drive levels of the PFI
signals are listed in the NI USB-621x Specifications.
Using PFI Terminals as Timing Input Signals
Use PFI terminals to route external timing signals to many different
USB-621x functions. Each input PFI terminal can be routed to any of the
following signals:
• AI Convert Clock (ai/ConvertClock)
• AI Sample Clock (ai/SampleClock)
• AI Start Trigger (ai/StartTrigger)
• AI Reference Trigger (ai/ReferenceTrigger)
• AI Pause Trigger (ai/PauseTrigger)
• AI Sample Clock Timebase (ai/SampleClockTimebase)
• AO Start Trigger (ao/StartTrigger)
• AO Sample Clock (ao/SampleClock)
Timing Signals
Direction Control
I/O Protection
47 k Ω Pull-Down
PFI/DIO Pin
Static DO
Buffer
Isolation
Barrier
(USB-6215/
6216/6218
devices only)
Digital
Isolators