Changing SPI pins

Projects Programming
1

I am working on building for an Uno, a shield PCB with a chip that runs SPI. The chip is surface mount and I would like to make the traces leading to it as simple as possible.

My question is, can I move the SPI pins to any digital pin that I want? I found a code that ebw44 posted in the storage section and I want to know if I can modify it to work with Uno? I am guessing the biggest difference would be just setting the pins numbers between 2-13.

Any suggestions would be great,
Mark

The code is most likely out of order, I have more saved but, the rest is specific to his application.

void setupExternalADC(){ 
 pinMode(SELPIN, OUTPUT); 
 pinMode(DATAOUT, OUTPUT); 
 pinMode(DATAIN, INPUT); 
 pinMode(SPICLOCK, OUTPUT); 
 //disable device to start with 
 digitalWrite(SELPIN,HIGH); 
 digitalWrite(DATAOUT,LOW); 
 digitalWrite(SPICLOCK,LOW); 
} 

there is an header file for pin configuration
#define SELPIN 25 //Selection Pin 
#define DATAOUT 24//MOSI 
#define DATAIN  26//MISO 
#define SPICLOCK  22//Clock
2

I think you need to post more of the code, but it appears from that bit that other parts of the code are bit-banging SPI, rather than using the hardware SPI. Hardware SPI is implemented on specific pins that vary by board type. The hardware SPI pins can not be changed without a soldering iron.

3

PaulS, I think you are correct, he is doing some sort of bit-banging SPI. I have not reached a full understand how it is done yet.

Thank you for the response. I am now leaning toward making the traces as necessary rather than adding more complex code.

Here is the rest of the code that ebw44 posted.

int read_adc(int channel){
  int adcvalue = 0;
  byte commandbits = B11000000; //command bits - start, mode, chn (3), dont care (3)

  //allow channel selection
  commandbits|=((channel-1)<<3);

  digitalWrite(SELPIN,LOW); //Select adc
  // setup bits to be written
  for (int i=7; i>=3; i--){
    digitalWrite(DATAOUT,commandbits&1<<i);
    //cycle clock
    digitalWrite(SPICLOCK,HIGH);
    digitalWrite(SPICLOCK,LOW);    
  }

  digitalWrite(SPICLOCK,HIGH);    //ignores 2 null bits
  digitalWrite(SPICLOCK,LOW);
  digitalWrite(SPICLOCK,HIGH);  
  digitalWrite(SPICLOCK,LOW);

  //read bits from adc
  for (int i=11; i>=0; i--){
    adcvalue+=digitalRead(DATAIN)<<i;
    //cycle clock
    digitalWrite(SPICLOCK,HIGH);
    digitalWrite(SPICLOCK,LOW);
  }
  digitalWrite(SELPIN, HIGH); //turn off device
  return adcvalue;
}
4

PaulS:
I think you need to post more of the code, but it appears from that bit that other parts of the code are bit-banging SPI, rather than using the hardware SPI. Hardware SPI is implemented on specific pins that vary by board type. The hardware SPI pins can not be changed without a soldering iron.

Or even WITH a soldering iron... XD

Edit: Read too fast, thought you meant the chip...

5

I think you are correct, he is doing some sort of bit-banging SPI.

That code is how you bit-bang SPI. So, why not use the hardware SPI method (and pins)?

6

Using digitalWrite() to bit bang SPI is going to be much slower than the hardware SPI, if this matters. Direct port manipulation can give a big speed up if the hardware SPI is out of the question.

7

PaulS:

I think you are correct, he is doing some sort of bit-banging SPI.

That code is how you bit-bang SPI. So, why not use the hardware SPI method (and pins)?

After reading all of the replies, I plan to make the hardware SPI pins work and adjust my PCB traces to get to the pins.

Thanks for all the help,
Mark