I2C extender connected on TAG4 startup

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Anonymous
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Hi all,

I am having problems starting the board when an I2C device is connected (GND, VCC and one or both of CLK and SDA) to J9. Even when I comment out all code that uses I2C and P2/P8 initialization, the board just won't start (on a coin cell battery) if external I2C is initially connected. Once started, I can connect the external I2C device no problem. Any ideas how to fix this?

Thanks,

Filipp

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1 Solution

The original team that designed this board is no longer with us, but I did find one individual that supported the PCB design and he shared the following guidance.

The I2C expander caused a reverse current during initialization that prevented the I2C bus from working properly; to counter this, one needs to connect the I2C expander after initialization.

In addition, he said to make sure on SW8, only positions 1,3,5 are selected (i.e. select EEPROM). Since I2C and SPI are sharing the same pins, you want to make sure only I2C is used. Once SPI is selected, the pins cannot be used for I2C until you re-initialize.

Hope this helps.

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