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AduM2250 not working

I am communicating over I2C between two PIC24FJ microcontrollers (one as master, one as slave) with the AduM2250 in between them.  My schematic is attached.  My software works fine when i communicate between the two microcontrollers without the AduM2250 between them.  I have the master sending the slave some data and then the master requests a response from the slave.  The problem I am having is that communication from the master to the slave works ok (most of the time all the bytes are transferred correctly, but sometimes the slave misses the interrupt or gets hung up).  The main problem is that the master is not receiving the correct data back from the slave.  I will get the first 2-4 bytes back correctly and then the rest is just garbage (and sometimes I only get garbage).  Also sometimes the slave seems to hang up on the TBF flag not being cleared and then it seems to holding the bus low.  Any ideas on what is going on?  I have side 1 as the master and side 2 as the slave.  

IsolatedI2Ccircuit.pdf
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  • Hi Kathryn,

    It looks like channel 2 has AC coupling on. See the ~ symbol on the bottom line. This should be set to DC coupled for looking at these signals. Also, the gnd alligator clip or reference point has to be attached to the local gnd. For example, when looking at the ADuM2250 SCL2 pin, make sure the probe gnd is connected to GND2 (and not GND1). This may explain the strange clock signal. 

    Can you do a capture of both SDA1 and SDA2 pins at once? And SCL1 and SCL2 pins at once? 

    Regards,

    Jason

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  • Hi Kathryn,

    It looks like channel 2 has AC coupling on. See the ~ symbol on the bottom line. This should be set to DC coupled for looking at these signals. Also, the gnd alligator clip or reference point has to be attached to the local gnd. For example, when looking at the ADuM2250 SCL2 pin, make sure the probe gnd is connected to GND2 (and not GND1). This may explain the strange clock signal. 

    Can you do a capture of both SDA1 and SDA2 pins at once? And SCL1 and SCL2 pins at once? 

    Regards,

    Jason

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