SPI Communication is not working in NRF52840

RE: SPI Communication is not working in NRF52840

SilasV — Mon, 16 Aug 2021 17:13:42 GMT

here are some points:

1. No need to have pullup resistors on SPI i/o lines

2. The default SPI config - NRF_DRV_SPI_DEFAULT_CONFIG has mode set to NRF_DRV_SPI_MODE_0, you are not setting this to NRF_DRV_SPI_MODE_1. You should run the SPI with frequency like 1Mhz, the default NRF_DRV_SPI_FREQ_4M (4Mhz)

3. When you assign a CS pin to SPI, this pin is controlled by the SPI instance, no need to add any code for that.

4. The reference manual of ADS1118 suggests series resistor of 50ohm on each SPI l/o lines to provide short circuit protection.

5. Also the DRDY / Dout pin on nRF should be configured as falling edge triggered interrupt input.

6. Since either config register or conversion register are 16bit type, you need to send 2 bytes , also the MSB goes first when writing / receiving the data.

There are two ways to config the device and read conversion values: 32bit mode or 16bit mode. 32bit is reading config register and followed by conversion register. If reading config register is not required, then use 16bit mode, which sends the config register set value (tx) and at the same time receive conversion value.

For 32bit, you can send 4 bytes, tx_buf first two bytes represent config register values, and rx_buf will receive conversion data (2 bytes) followed by configReg value (2bytes).

First using 32bit mode: if configRegister = 0x058B (this is POR value), then since your buffers are 8bit

m_tx_buf[0] = configRegister >> 8;

m_tx_buf[1] = configRegister;

and then if you run the following SPI transfer commands, you should receive the same value in rx_buffer. If you read the same value, then your SPI is working fine.

nrf_drv_spi_transfer(&spi, m_tx_buf, 2, m_rx_buf, 4)

the above will transmits 2 bytes which is the config register value and received data will be 4 bytes, this would be the conversion value followed by config reg value. The values in rx_buf[2] and rx_buf[3] should be same as tx_buf sent.

For 16bit mode which is just reading the conversion data after DRDY is low, you can just send current config reg value (2bytes) and receive conversion data (2bytes) at the same time

nrf_drv_spi_transfer(&spi, m_tx_buf, 2, m_rx_buf, 2)

hope above helps.

RE: SPI Communication is not working in NRF52840

sharmelaraju — Mon, 16 Aug 2021 05:51:20 GMT

Thanks for the reply.

We have checked that we are measuring on the correct pins and there is no problem in pin assignment also .But the doubt is the programming can you pleas tell me whether the programming is correct or do i need to make changes in the program as i had initialized the ads1118 of the configuration registers in the program. I am attaching the program file here.

The doubt is do we need to pull up the pin of MISO,MOSI, CS pin in hardware?

devzone.nordicsemi.com/.../SPI_5F00_DONGLLE.txt devzone.nordicsemi.com/.../ADS118.ci

Initially when we have tried we were getting as zero as output when we have changed the NRFX_SPIM_MISO_PULL_CFG 1 (PULL DOWN) to NRFX_SPIM_MISO_PULL_CFG 3 (PULL UP) in software

we are reading as 00 and FF in the output . Can you please give me the suggestion where i am going wrong.

RE: SPI Communication is not working in NRF52840

SilasV — Tue, 10 Aug 2021 14:17:30 GMT

I can say the following after going through your code:

1. I think you need to study the ADS1118 datasheet carefully.

2. The Dout data frame is either 16bit or 32bit. When you are using single-shot conversion by using CS pin, the data frame would be 16bit.

3. There is no code to initialize the config register.

4. Config register is of R/W type, so you can test if the SPI communication is working ok or not by writing to config register and reading it back and confirming.

5. After confirming communication is working ok, you can set up ADS1118 for measuring the temperature by using its internal temperature sensor, which will avoid any external circuit issues. If you can read the current temperature correctly then the device is working fine. Then you can go ahead with reading analog inputs.

6. if the above steps do not work and if this is your custom board, you need to make sure the chip is soldered correctly. you should also provide test points on board for easy access to various pins of the chip.

7. Further you can also run the code in debug more in SES, and step through each code and see if the SPI pins have expected logic on logic analyzer / oscilloscope. you can also see if the code goes into any hard faults.

hope the above helps..

RE: SPI Communication is not working in NRF52840

Jared — Tue, 10 Aug 2021 12:14:09 GMT

Hi,

My guess is that either the program is asserting or you're not measuring on the correct pins. The latter might be due to using the wrong board file or pin assignments etc. The former can be checked by using an external debugger and debugging the fw on the Dongle.

regards

Jared

RE: SPI Communication is not working in NRF52840

sharmelaraju — Tue, 10 Aug 2021 11:48:30 GMT

Thanks for the reply.

The SPI mode is already set to 1 ,and the chip select is also made as active low ,but we have not waited for the DRDY pin to low and now we are waiting for the DRDY pin to low. When we made this change in the program now we are reading as FF value from the MISO pin.

Now the problem is i need to read the ADC channel 0 since it is connected to ground it should read as zero but we are reading as FF when we read the other ADC channel it is also reading as zero. Even we have changed the PGA gain ,Data sampling rate to different value but whatever the value we have changed in the configuration register we are reading as FF.

So when we checked in the oscilloscope the chip select is high, the MISO pin also high but in the clock signal we are not getting clock , and in the MOSI signal the signal is low.

Can you please tell me where we are going wrong . I am attacdevzone.nordicsemi.com/.../SPI_5F00_1_5F00_DONGLE.txthing the code here.

Please help me to resolve this problem.

RE: SPI Communication is not working in NRF52840

SilasV — Mon, 09 Aug 2021 14:52:43 GMT

There are a few checks you can do:

1. Have you configured the SPI for Mode 1 (as per the ADS1118 datasheet - the SPI mode should be 1)? Default SPI config has Mode 0.

2. Make sure to configure CS as active low.

3. Also need to wait for Dout/DRDY to transition to low, which means conversion data is now available

4. after making sure of above, check the signals on the SPI pins on ADS1118 with help of oscilloscope / logic analyzer. You can also use PPK2 logic ports. Make sure the signals are as expected.