Question
Inquiry Description:We implemented the ADXL345 on a board. It interfaces with an Altera Cyclone VFPGA. The ADXL345 datasheet says that the CS input must either be connected toVDD or else to an external controller otherwise it may not be possible tocommunicate with the device. On our board it is connected directly to theFPGA. We found that we were not able to communicate with the device until weadded a pull-down resistor on the pin. We checked the schematic of anevaluation board with the device and an FPGA and found that it has thepull-down as well. We have the same device on another board of ours where itinterfaces with a microcontroller and it is fine without the pull-down. Shouldwe need this resistor? It means we need a redesign of the board and it doesn'tsay anywhere in the datasheet that we should need it.
Answer
Please find below an example for connecting ADXL345 with a microcontroller(ADuC7026).
Other microcontrollers or processor types could be used to access ADXL345 withthe similar circuit connections as shown above.