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Using the SMB Connector for Digital I/O or Drift Compensation on cRIO-901x and 9074 Controllers

Hardware: CompactRIO>>Controllers>>cRIO-9012, CompactRIO>>Controllers>>cRIO-9014

Problem:
The Operating Instructions manual for cRIO-9012/9014/9074 controllers states the following:
"The software that supports GPS drift-correction and other digital I/O through the SMB connector was not available when this manual was published. Please contact National Instruments for more information."

How can I use the SMB connector on these controllers?

Solution:
You can use the SMB connector of cRIO-9012/9014/9074 controllers to connect a digital device to the controller. For example, if you connect the pulse-per-second (PPS) output of a GPS device to the SMB connector of a cRIO-9012/9014/9074 , you can use the GPS device to correct for drift of the system clock of the controller. You can also use the SMB connector as a general purpose digital I/O line. 

Using the SMB Pin as General Purpose Digital I/O
To use the SMB pin as a general purpose digital I/O line, download the set of VIs attached below in the file 901x SMB Pin.zip. This zipped directory contains 4 VIs to read, write, set, and get the SMB pin mode.

Using the SMB Pin for GPS drift-correction
To use the SMB pin for GPS drift-correction, add the following lines to the ni-rt.ini file for the controller. You will need to FTP this file onto a Windows machine, make the changes, and FTP the modified file back to the controller.  After updating the ni-rt.ini file, the cRIO-901x controller will automatically implement the GPS drift-correct based on the PPS input.

[Time Sync]
source.rtc.enable=True
source.dio.enable = True
source_priority=dio;rtc;
source.dio.hz = 1.0

You can also set the expected frequency of the input. The default is 1.0 Hz. For example, If 2 Hz is the expected frequency, change the last line to source.dio.hz = 2.0. 

Note: If the PPS signal is lost or the error is greater than 10% off from the expected frequency, then the drift-correction measurements will not be used to correct the clock time on the Embedded Controller.

The attached project 901x Drift Correction.zip can be used to observe the operation of the drift compensation by connecting a digital output from a module such as an NI 9403 to the SMB connector on the controller.

Related Links:
Tutorial:  Software Support for CompactRIO, CompactDAQ, Single-Board RIO, and R Series Device
KnowledgeBase 4CQFC9LX: Using the Internal Real-Time Clock on cRIO-901x Controllers
Product Manuals: CompactRIO cRIO-9012/9014 Operating Instructions and Specifications
Product Manuals: CompactRIO cRIO-9072/3/4 Operating Instructions and Specifications


Attachments:


- 901x SMB Pin 8.2.zip
- 901x Drift Correction.zip


Report Date: 05/04/2007
Last Updated: 11/26/2008
Document ID: 493BIHLX

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