Arduino Due SPI Clock not changing

Official Hardware Mega Due
1

I am trying to use SPI on the Arduino Due rev3 located at ICSP header/SPI. I set it up based on the library, but I don't seem to have control SPI clock, clock phase, frequency etc....On power up, the clock pin is low, and it is always low to high phase when I specifically changed the mode to SPI_MODE2. It is disregarding it.

In the setup() function I dump the code below . I have tried the different ways to set it up, but all I get is a clock on Pin2 (see references below) 4MHz, MODE0, and I can't control the phase or the frequency.

//SPISettings mySetting(1000000, MSBFIRST, SPI_MODE3);
  //SPI.beginTransaction(mySetting);
  //SPI.beginTransaction(SPISettings(5000000, MSBFIRST, SPI_MODE0));
  SPI.setClockDivider(84);                      //84MHz/84 = 1MHz
  SPI.setDataMode(SPI_MODE2);
  SPI.setBitOrder(MSBFIRST);
  SPI.begin();  

void ReadADC(char AdcChannel)
{
  CtrlReg = (AdcChannel << 3);                              //Select the ADC channel by writing the register
  digitalWrite(AdcCSPin, LOW);
  Temp1=SPI.transfer16(CtrlReg);                        //Bring CS low
  digitalWrite(AdcCSPin, HIGH);
}

The MCU SPI CLK is at MCU PIN PA27.. Is there anything that I am doing wrong?
why wouldn't this code work? Is there any underlying setup I need to do first?

When I put the scope on the clock, it is coming out, and I see two transfer of 8 bits. I thought the SPI.tranfer16 would do 16 clock cycles without any delays in between. Is there a way to do 16 bit transfer without delays?

  1. why is the code not working?
  2. How do I transfer continuous 16 clock cycles?
3

begin() must be called before setDataMode and others.

1 Like
4

OK then...

5

Do you know how to transmit 16 bits continously instead of two transfers of 8bits?

6

transfer16()

7

That transfers in two packets of 8 bits with an annoying delay between the packets. I mean 16clock cycles uninterrupted with the same period. Thanks for replying.

8

Arduino code does not support real 16 bit transfers, you have to implement it yourself. You can change word size in SPI Chip Select Register aka SPI_CSR and I assume you have to implement your own transfer function.

ps: I understand if this operation is annoying, but please tell me at the end if it was worth the work invested

9

Sadly I have to use this arduino to characterize time sensitive adc acquisitions not for hobbies for real hardware which I cannot discuss here. Suffice to say for a lot of folks this is adequate. I happen to not be in 98 percentile where every microsecond matters. Thank you for the reply.

10

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