National Instruments USB-621 Series User Manual page 6

Contents
Chapter 3
Connector and LED Information
I/O Connector Signal Descriptions................................................................................ 3-1
+5 V Power.................................................................................................................... 3-3
+5 V Power as an Output ................................................................................ 3-3
+5 V Power as an Input................................................................................... 3-3
USB Chassis Ground..................................................................................................... 3-4
USB Device Fuse Replacement..................................................................................... 3-4
PWR/ACT LED Indicator ............................................................................................. 3-6
Chapter 4
Analog Input
Analog Input Range....................................................................................................... 4-2
Analog Input Ground-Reference Settings ..................................................................... 4-3
Configuring AI Ground-Reference Settings in Software................................ 4-5
Multichannel Scanning Considerations......................................................................... 4-5
Analog Input Data Acquisition Methods....................................................................... 4-8
Analog Input Digital Triggering.................................................................................... 4-10
Field Wiring Considerations.......................................................................................... 4-10
Analog Input Timing Signals ........................................................................................ 4-11
AI Sample Clock Signal.................................................................................. 4-14
AI Sample Clock Timebase Signal ................................................................. 4-15
AI Convert Clock Signal................................................................................. 4-16
AI Convert Clock Timebase Signal ................................................................ 4-19
AI Hold Complete Event Signal ..................................................................... 4-19
AI Start Trigger Signal.................................................................................... 4-20
AI Reference Trigger Signal ........................................................................... 4-21
AI Pause Trigger Signal .................................................................................. 4-22
NI USB-621x User Manual
Using an Internal Source .................................................................. 4-14
Using an External Source ................................................................. 4-14
Routing AI Sample Clock to an Output Terminal ............................ 4-14
Other Timing Requirements ............................................................. 4-14
Using an Internal Source .................................................................. 4-16
Using an External Source ................................................................. 4-16
Routing AI Convert Clock to an Output Terminal ........................... 4-16
Using a Delay from Sample Clock to Convert Clock ...................... 4-17
Other Timing Requirements ............................................................. 4-17
Using a Digital Source...................................................................... 4-20
Routing AI Start Trigger to an Output Terminal .............................. 4-20
Using a Digital Source...................................................................... 4-22
Routing AI Reference Trigger to an Output Terminal ..................... 4-22
Using a Digital Source...................................................................... 4-22
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