I want to test the SPI communication bewteen the Duemilanove(Atmega328p) and ATMega1280. I make the Duemilanove as the Master and ATMega1280 as Slave. The wiring and the code are listed below (Define the macro SPI_MASTER_MODEL and SPI_SLAVE_MODEL for the Master and Slave side code respectively). Through the PC serial monitor, I found the received data from SPI is wrong. Does anyone can point out the error in my code? Thanks in andvance.
Wiring
ATMega328p ATMega1280
SS(10) -------------- SS(53)
MOSI(11)-------------- MOSI(51)
MISO(12)-------------- MISO(50)
SCK(13) -------------- SCK(52)
Code
/**************************************************************************************
Functionality:
Two Arduinos communicate via SPI.One is master, the other is slave.
atmega 328p works as master
atmega 1280 works as slave.The circuit:
Use atmega 328p and atmega 1280 as test boards.
ATMega328p ATMega1280
SS(10) -------------- SS(53)
MOSI(11)-------------- MOSI(51)
MISO(12)-------------- MISO(50)
SCK(13) -------------- SCK(52)Connect the atmega 328p/1280 board to PC through USB. Monitor the data from it.
***************************************************************************************/
#include "pins_arduino.h"
void SPI_Init(void);
unsigned char SPI_ReadWrite(unsigned char data);#define SPI_MASTER_MODEL
//#define SPI_SLAVE_MODEL#if defined(SPI_MASTER_MODEL)
const char* pSPIStr = "Master";
#else
const char* pSPIStr = "Slavee";// The same length
#endif// init as SPI-Master
void SPI_MASTER_Init(void) {
pinMode(SCK,OUTPUT);
pinMode(MOSI,OUTPUT);
pinMode(SS,OUTPUT);
pinMode(MISO,INPUT);// INIT interface, Master, set clock rate fck/4
// SPCR – SPI Control Register
//
// SPE: SPI Enable. When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI operations.
// MSTR: Master/Slave Select. This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic zero.
// If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared, and SPIF in SPSR will become set.
// The user will then have to set MSTR to re-enable SPI Master mode.
// SPR1, SPR0: SPI Clock Rate Select 1 and 0. These two bits control the SCK rate of the device configured as a Master.
// SPR1 and SPR0 have no effect on the Slave.SPCR = (1<<SPE)|(1<<MSTR)|(0<<SPR0)|(0<<SPR1);
// enable double rate
// SPSR – SPI Status Register
//
// SPI2X: Double SPI Speed Bit.When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI
// is in Master model.
SPSR = (1<<SPI2X); // we will now gain fck/2 instead of fck/4
}void SPI_SLAVE_Init(void) {
pinMode(SCK,INPUT);
pinMode(MOSI,INPUT);
pinMode(SS,INPUT);
pinMode(MISO,OUTPUT);// INIT interface, Slave, set clock rate fck/4
SPCR = (1<<SPE)|(0<<MSTR)|(0<<SPR0)|(0<<SPR1);
// enable double rate
SPSR = (1<<SPI2X); // we will now gain fck/2 instead of fck/4
}unsigned char SPI_ReadWrite(unsigned char data) {
// set data to send into SPI data register
// SPDR – SPI Data Register. The SPI Data Register is a read/write register used for data transfer between the Register File
// and the SPI Shift Register. Writing to the register initiates data transmission. Reading the register causes
// the Shift Register Receive buffer to be read.
SPDR = data;
// Wait for transmission complete
// SPIF: SPI Interrupt Flag.
// When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in
// SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is
// in Master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing the
// corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the
// SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
while(!(SPSR & (1<<SPIF)));
// return data read from SPI (if any)
return SPDR;
}void setup() {
#if defined(SPI_MASTER_MODEL)
SPI_MASTER_Init();
#else
SPI_SLAVE_Init();
#endifSerial.begin(9600);
}
void loop(){
Serial.println();
Serial.println("SPI communication begin.");
Serial.println();
const char str = pSPIStr;
while (*str)
{
unsigned char dataBuffer = (unsigned char)(*str);
Serial.print(dataBuffer, BYTE);
dataBuffer = SPI_ReadWrite(dataBuffer);
str++;
Serial.print(dataBuffer, BYTE);
}
}
