usb 8451 I2C

[lec]

Hi,

I am using LabView 8.0 with an NI USB 8451 I2C device. The problem I'm having is once a DUT fails it causes the next DUT to fail also. Very repeatable. Its as if there is a buffer that still has some data in it from the first failure or an error flag has been set. I have to restart the program to clear up the problem. I'm not sure if its a LabView error flag or an I2C "buffer" problem. Also, is there a way to initialize the 8451 so I can always start from a known good status? I have the same problem with the GPIB driver and the HP meter buffer but I've done a workaround by reading the meter twice. The first read is garbage but it clears the HP buffer so the second read is valid.
Thanks in advance for your help.

Larry Clifford
Precision Linear Systems

[Daklu]

I had the same problem in 8.2 that I was never able to resolve.  Is the 8451 the only master on the bus or are you tapping into a line that already has a master?  I found the 8451 worked very well when it was the only master but problems popped up on a multi-master setup.  I contacted NI tech support and they assured me the 8451 adheres to the I2C multi-master specs.  Scope traces I took seemed to verify that.  I believe the problem was that the native master on the bus didn't handle multi-master mode correctly.

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