0

I have a master and a slave (both are arduino UNO) connected through SPI connected. I want to transmit a character to the slave and receive true or false to the master. The transmission is working perfectly. If I send '2', slave is receiving '2'. When I try to transmit an integer from slave to master, the master is always receiving some arbitrary number like 128 or 255.

Master Code:

void setup() {
  Serial.begin(9600);
  Serial.println("Master");
  digitalWrite(SS,HIGH);
  SPI.begin();
  SPI.setClockDivider(SPI_CLOCK_DIV8);
}
void loop() {
  digitalWrite(SS,LOW);  //  Slave select to low
  received1 = SPI.transfer(test);  // test is a variable which is '2'. The data received by master is stored in received1 variable which is char.
  Serial.println(received1);  
  digitalWrite(SS,HIGH);  
}

Slave code:

void setup() {
  Serial.begin(9600);
  Serial.println("Slave");
  pinMode(MISO,OUTPUT);
  SPCR |= _BV(SPE);
  process = false;
  SPI.attachInterrupt();  
}
ISR(SPI_STC_vect){
  received = SPDR;  // the data received by slave is slored in **received** variable(the variable is char type)
  Serial.println(received);
  process = true;
}
void loop() {
  if(process){
    SPDR = jj;  // Updating SPDR to send data from slave. jj is char type
    process = false;
  } 
}
Improve this question
2
  • The most important part, declaration of variable process, is not here. Is it volatile? Also do you realize that SPDR on slave must be set before the master starts transmission? Commented Jul 7, 2017 at 12:11
  • Sorry for not mentioning about process. It's a boolean variable which will be true when something is received by slave. Commented Jul 7, 2017 at 12:32

1 Answer 1

Reset to default
0

I have found a solution for this problem in a blog.

Link: http://www.gammon.com.au/forum/?id=10892

I modified my master code and got my desired result.

Master code:

byte transferAndWait (const byte what)
{
  byte a = SPI.transfer (what);
  delayMicroseconds (2000);
  return a;
} // end of transferAndWait

void loop() {
  digitalWrite(SS,LOW);
  transferAndWait (10);  
  received1 = transferAndWait (11);
  digitalWrite(SS,HIGH);
  Serial.println(received1);
}

The response will be "collected" next time through the loop. That's why we need to keep a dummy transferAndWait() function first and then the result of that transfer will be stored in received1 variable.

Improve this answer
1
  • Please accept your own answer if it solved your problem, otherwise Stack Exchange throws it up from time to time as an unsolved question. Commented Aug 7, 2017 at 9:25

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.