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8476
denikar
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11-05-2013 08:43 AM
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Hi all,
I am working with the USB-8476 and have a question about signal quality. Attached is a screenshot of the output of the module for reference. The 8476 is configured in master mode.
The screenshot illustrates the LIN bus output. Note the output remains the same regardless of if it is connected to the LIN bus or not. As you can see from the image, the bus bits do not appear to be reaching their voltage rails, and this is causing occasional LIN bus errors / retries.
Has anyone seen this issue before or have ideas as to why the signal quality is so poor? I have tried another 8476 and the signal looks the same.
Thanks,
Tim
GPIB_Guru
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11-05-2013 08:44 AM
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Do you have master termination enabled?
11-05-2013 08:49 AM
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Thanks for the reply. Our software group says they have it enabled, and from measurements it appears the pullup is there. Using a current probe I see ~12mA during low activations, which is about a 1k pullup.
Esteban.R
NI Employee (retired)
11-06-2013 05:50 PM
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Hi denikar
I will like to ask you some questions in order to have more information about what might be causing this issue.
How are you measuring that signal? Which is the sampling rate of that oscilloscope?
How long is the cable that you are using to communicate the master with the slave?
What kind of environment do you have in the lab or around the devices?
Which power supply are you using for the LIN communication?
Regards
Esteban R.
11-07-2013 06:51 AM
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Hi Esteban,
Thanks for the reply. Answers to your questions are below.
How are you measuring that signal? Which is the sampling rate of that oscilloscope?
The scope sampling rate for that capture was 1 million samples per second.
How long is the cable that you are using to communicate the master with the slave?
About 12" long. It goes immediately to a fiber-optic LIN bridge. The signal looks the same even with the cable disconnected from the fiber-optic bridge.
What kind of environment do you have in the lab or around the devices?
It is in a control room. Room temperature, controlled humidity, no high current devices or cables nearby.
Which power supply are you using for the LIN communication?
A standard linear laboratory 3A bench top power supply, set to 12V.
Regards,
Tim
Eric-J
NI Employee (retired)
11-08-2013 06:07 PM
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Hi,
What is the status of each of the LEDs on the 8476 during operation?
Applications Engineer
National Instruments
National Instruments
