SPI communication with ADXL372

RE: SPI communication with ADXL372

matty — Wed, 29 Jan 2020 23:27:06 GMT

hmolesworth, Thank you! Those are great ideas. Ever since I burnt a Cypress chip many years ago, I don't connect anything without double checking. Also Analog Devices is assiduous in there warnings about supply voltages. I will implement your ideas and report back. Thanks again.

5 hours latter and there is joy in Mudville! To paraphrase Marco in Case ID 116690, I was concentrating on software so much I forgot about the hardware. Thank you hmolesworth. Used shorter jumper wires and gave SCK and MOSI 5mA via H0HI. Prototyping proceeds and this shouldn't be a problem when the nRF52480 and the ADXL372 are on the same board.

Also check out Case ID 211119 for good S0S1 vs H0H1 explanation.

RE: SPI communication with ADXL372

hmolesworth — Wed, 29 Jan 2020 16:47:11 GMT

You mention testing with an Arduino; hopefully that was with 3.5 volt i/o and not 5 volt given the max supply to the ADXL372 is 3.5 volts. The implication is that the ADXL372 is connected by some leads rather than being close to the nRF52 via PCB traces. The Arduino also has higher pin drive, I imagine, so I would suggest trying boosted drive levels on the nRF52 after the SPI port is initialised with nrf_drv_spi_init() as that function uses S0S1 or standard drive. Using a higher SCK frequency of 8MHz also shows more clearly on a 'scope any edge bounce caused by the transmission lines being unterminated (I kid you not, this happens).

// Change nRF52 driven pins to High Drive 0 and 1:
  nrf_gpio_cfg(SPI0_MOSI_PIN. NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
  nrf_gpio_cfg(SPI0_SCK_PIN,  NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
  nrf_gpio_cfg(SPI0_SS_PIN,   NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);

RE: SPI communication with ADXL372

Kenneth — Wed, 29 Jan 2020 10:28:49 GMT

Hi,

Looking at the code, I can't find any obvious wrong no. Seems you have very relaxed timing, so that should not be an issue. I guess you can try to connect MISO to MOSI without the adxl372, and see that you are loop backing the data as expected. I think waiting for the logic analyzer is the best way forward, then you can compare working and failing (it may for instance be polarity and phase of the SPI, possible voltage levels, or anything else at the moment unfortunately).

Best regards,
Kenneth