Read from 18-bit ADC using SPI

[nathansowie]

Hi everyone,

I am trying to read values from an 18-bit ADC using SPI and LPC54608.

I would like to know what would be the best way to read the values from the ADC.

Here is the code I wrote:

uint32_t readSPIvalueInitSPI4(){
   return readSPIvalueInit2(&SPI4_InterruptDriverState);
}

uint32_t readSPIvalueInit2(cmsis_spi_interrupt_driver_state_t *spi){

   return readSPIvalue(spi->resource->base);
}

uint32_t readSPIvalue(SPI_Type *base){

   base->CFG |= (1 << 8);             // polarity SSEL0 - active high
   base->DLY |= (0x8 << 8);          // End Of Frame delay - 8 clock times inserted

   uint32_t readFIFO = ADC_LT2336(base);

   return readFIFO;

}

uint32_t ADC_LT2336(SPI_Type *base){

   base->FIFOWR = 15 | 0xf0e0000;       // data = 15 + Assert SSL0, de-assert SSL[1,2,3], no-EOT                                                                 // (EndOfTransfer de-assert), length = 16

   base->FIFOWR = 15 | 0x31e0000;      // data = 15 + Assert SSL0, de-assert SSL[1,2,3], EOT (EndOfTransfer                                                                 // de-assert), End Of Frame delay = 15 CLK, length = 4

   uint_32_t read_MSB = base->FIFORD;
   uint_32_t read_LSB = base->FIFORD;

   return read_MSB;                     // only returning the MSB because I don't need the last 2 bits

}

int main(void) {

   uint32_t ADCvalue = readSPIvalueInitSPI4();

}

In the "ADC_LT2336(SPI_Type *base)" function, I am not sure whether I should read MSB before sending the second write command, or if I should do like in the code above (1st send the two write commands, and then two read commands).

If it can be of any help, the ADC I am using is the LTC2336 from Analog Devices, and here is the link to the datasheet of this ADC: http://www.analog.com/media/en/technical-documentation/data-sheets/233618fa.pdf 

Thanks in advance,

Nathan Sowie

[Hui_Ma]

Hi,

The LPC54608 SPI function supports separate transmit and receive FIFOs with 8 entries each.

From your application, you only use two receive FIFO.

That will be ok for your both operations ( read MSB before sending the second write command, or 1st send the two write commands, and then two read commands).

Wish it helps.

Have a great day,
Mike

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[nathansowie]

Hi,

Thank you for this answer, this will surely help !

Thanks,

Nathan