Send numbers bigger than 256 by SPI

Question

How can i send numbers like 300 or 1024 ?

I'm using the recommendation of the atmel's manual.

void SpiTransmitir(unsigned char data)
{
 SPDR = data;
 while(!(SPSR & (1<<SPIF)));//{Serial.println("While");}
}

I imagined that one bit shift could be the solution, but it still fails.

Answer 1

You need to send two bytes - a high byte and a low byte.

There are two things you need to know with SPI:

1. You must wait for one byte to finish transmitting before you send the next
2. The whole transaction needs to be wrapped with a digital chip select signal.

So you have:

1. Chip Select idles HIGH
2. You lower Chip Select
3. You send one byte
4. You send the other byte
5. You raise chip select

At the receiver you:

1. Wait for chip select to go low
2. Receive one byte
3. Receive a second byte
4. Chip Select rises
5. You combine the two bytes together into one integer.

• Victor Reis: Can i use the arduino's functions lowByte() highByte()?
• Majenko: You can, yes. Or just do it manually with >> 8 and & 0xFF

Answer 2

Try to join the numbers as follows:

#define NUMERO 342
void setup() {
 Serial.begin(9600);
 Serial.println(NUMERO, BIN); // Mostra valor do número em binário
 uint8_t MSB = 0, LSB = 0; // Dois números de 8 bits
 uint16_t junta = 0; // Valor junto em 16 bits
 MSB = NUMERO >> 4;
 LSB = NUMERO << 4;
 junta = (MSB << 4) | (LSB >> 4) ;
 Serial.println(junta, BIN);
}
void loop() {}