SPI difficulty

Projects Networking, Protocols, and Devices
1

Hi, I can't get the SPI function to work on my Nano. The code is here:

#include <SPI.h>

//Chip select for three DAC's
int CS1 = 10; 
int CS2 = 9;
int CS3 = 8;

// set up the speed, data order and data mode
SPISettings settings(10000000, MSBFIRST, SPI_MODE0); 

void setup() {
  pinMode (CS1, OUTPUT);
  digitalWrite(CS1, HIGH);
  pinMode (CS2, OUTPUT);
  digitalWrite(CS2, HIGH);
  pinMode (CS3, OUTPUT);
  digitalWrite(CS3, HIGH);

  // initialize SPI:
  SPI.begin();
}

void loop() {
  // SPI communication with DAC
  SPI.beginTransaction(settingsA);
  digitalWrite(CS1, LOW);
  digitalWrite(CS2, LOW);
  digitalWrite(CS3, LOW);
  SPI.transfer(127);
  SPI.transfer(127);
  digitalWrite(CS1, HIGH);
  digitalWrite(CS2, HIGH);
  digitalWrite(CS3, HIGH);
  SPI.endTransaction();
  
  delay(1000); 
}

I think it should be Mode0, but I've tried all modes and varying speeds also, and it still doesn't seem to work. The below code does work fine - does this way of doing it have disadvantages? Is it a lot slower for example?

Primarily though would appreciate if someone could point out what I am doing wrong in the above please

Many thanks

#define CS1 10
#define CS2 9
#define CS3 8
#define DIN 12
#define SCK 13

void setup() {
  // put your setup code here, to run once:
pinMode(CS1, OUTPUT);
pinMode(CS2, OUTPUT);
pinMode(CS3, OUTPUT);
pinMode(DIN, OUTPUT);
pinMode(SCK, OUTPUT);

digitalWrite(CS1, HIGH);
digitalWrite(CS2, HIGH);
digitalWrite(CS3, HIGH);
}

void loop() {
  // DAC1
digitalWrite(CS1, LOW);
delay(100);
//1011001100110011
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

digitalWrite(CS1, HIGH);

//DAC2
digitalWrite(CS2, LOW);
delay(100);
//1011001100110011
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

digitalWrite(CS2, HIGH);

//DAC3
digitalWrite(CS3, LOW);
delay(100);
//1011001100110011
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//0
digitalWrite(DIN, LOW);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);
//1
digitalWrite(DIN, HIGH);
digitalWrite(SCK, HIGH);
digitalWrite(SCK, LOW);

digitalWrite(CS3, HIGH);

delay(1000);
}
2

AFAIK you can only talk to one SPI slave at a time and to do that you should only set one of the CS lines LOW

...R

3

A Nano can't go over 8MHz SPI frequency. If you activate more than one SPI device at the same time (by pulling it's CS low) you might create a short circuit on the MISO line which can destroy the device.

4

As noted, 8000000 is the max speed for a Nano with a 16 MHz system clock.

Try moving this to After SPI.begin();

// set up the speed, data order and data mode
SPISettings settings(10000000, MSBFIRST, SPI_MODE0);

You might even try leaving it out altogether, the defaults are speed of 4000000, MSBFIRST, and SPI Mode 0. With the delay(1000); I doubt you'd notice the difference between 4000000 and 8000000.

I've never used these 2 lines, is that something new?
SPI.beginTransaction(settingsA);
and
SPI.endTransaction();

The MISO comment is not a concern as you do not appear to have MISO connected.

5

Yea, problem sorted, thanks for the help!

6

Mickey_blu_eyes:
Yea, problem sorted, thanks for the help!

Good idea, and very helpful to those in the future searching the forums, if you explainded what you did to sort the problem.

7

Sorry but I'd actually just got it wrongly connected. One of the first pinout diagrams that pops up on google for 'nano spi connections' is this one - which shows the mosi pin as D12, when it should be D11!!

Still, useful info about max speed and risks of talking to multiple slaves simlutaneously - thanks a lot!