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ADXL345 Eval Kit switch to 3-pin SPI

Question asked by JeffJway on May 28, 2013
Latest reply on May 29, 2013 by neilzhao



I have a question that to me should be simple, but I can't seem to find out how to do it.


I have the ADXL345 eval kit with satellite board. I notice, when using the evaluation GUI, that the IESB seems to communicate with the satellite board using 4-wire SPI. I derive this understanding from the fact that the initial register read of DATA_FORMAT is 0x00 and the documentation "ADXL345 ISEB User Guide.pdf" shows the inital jumper settings on the satellite board to be for 4-wire SPI.


I wish to know how to switch the Evaluation kit to use 3-wire SPI between the IESB and the satellite board (if this is even possible). I have shifted the jumper on the satellite to enable 3-wire SPI and I have written to the DATA_FORMAT register 0x40 to enable 3-wire communications. I am only using 1 Satellite board, thus the set-up is 1 master-1 slave. But after I have done so, I am unable to read or write to the satellite using the GUI's Configuration tab or read values in the Real-time measurement tab.


From what I know, the difference between the SPI 3-wire and 4-wire communications is the STE line that controls the communication for multiple Masters, thus switching 4-wire to 3-wire for a 1 master-1 slave setup should not need a hardware change.


Am I missing something? Should I have removed the jumper entirely instead of shifting it? Is it not possible (hard-coded GUI program, hard-wiring somewhere, etc) to do so? Or is my understanding of the whole scenario wrong?