SPI COMMUNICATION TUTORIAL etc.

Projects Programming
1

Arduino - Serial Peripheral Interface
Well tutorials in general have a number of mistakes but I view that as motivation to learn more and to dive into the topics. So far so good. But...
What's with the '\r' used here and in previous exercises??? It suppose to be a carriage return... ??? I digress here is what I could use you help on. Thanks
I am working on having two Arduino UNO R3's talking Master - Slave.
The wiring between the two are 10, 11, 12 and 13. Ground pin to Ground pin.
MASTER
#include <SPI.h>

void setup (void) {
Serial.begin(115200); //set baud rate to 115200 for usart
digitalWrite(SS, HIGH); // disable Slave Select
SPI.begin ();
SPI.setClockDivider(SPI_CLOCK_DIV8);//divide the clock by 8
}

void loop (void) {
char c;
digitalWrite(SS, LOW); // enable Slave Select
// send test string
for (const char * p = "Hello, world!\r" ; c = *p; p++) {
SPI.transfer (c);
Serial.println(c);
}
digitalWrite(SS, HIGH); // disable Slave Select
delay(2000);
}
SLAVE
#include <SPI.h>
char buff [50];
volatile byte indx;
volatile boolean process;

void setup (void) {
Serial.begin (115200);
pinMode(MISO, OUTPUT); // have to send on master in so it set as output
SPCR |= _BV(SPE); // turn on SPI in slave mode
indx = 0; // buffer empty
process = false;
SPI.attachInterrupt(); // turn on interrupt
}
ISR (SPI_STC_vect) // SPI interrupt routine
{
byte c = SPDR; // read byte from SPI Data Register
if (indx < sizeof buff) {
buff [indx++] = c; // save data in the next index in the array buff
if (c == '\r') //check for the end of the word
process = true;
}
}

void loop (void) {
if (process) {
process = false; //reset the process
Serial.println (buff); //print the array on serial monitor
indx= 0; //reset button to zero
}
}
OUTPUT
Master
H
e
l
l
o
,

w
o
r
l
d
!

⸮⸮⸮
⸮⸮,⸮⸮⸮ ⸮2B⸮⸮⸮K⸮⸮⸮⸮⸮⸮⸮
SLAVE
Nothing

2

buff should be volatile too

a cString needs to be null terminated so that you can safely print it (that will work if you send less than 49 bytes as your global buff is null initialized)

Side note:this

    if (c == '\r') //check for the end of the word
      process = true;

could be written

 process = (c == '\r');

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3

Thanks will get to it... thanks for the guidance.