Implementing SPI data transfer via low-level AVR methods

Host side:

 1 /*********************************

 2 Code function: Implement SPI data transmission (host side) through the underlying AVR method

 3. Creation time: 2016*10*17

 4. Use resources:

 5 Lower-level aTmega (AVR) library

 6 SPI three registers SPCR (control register), SPCR (status register), SPDR (data register)

 7 SPCR (SPI Control Register)

 8 7bit SPIE Chip select enable, SPIE = 1; chip select is invalid, SPIE = 0 chip select is valid (the host does not need chip select) (stand-alone communication also does not need chip select)

 9             6bit    SPE        

10             5bit    DORD    

11             4bit    MSTR    

12 3bit CPOL clock polarity, CPOL = 0 (clock idle is low level); CPOL = 1 (clock idle is high level)

13 2bit CPHA phase polarity, CPHA = 0 (indicates the first edge); CPHA = 1 (indicates the second edge); both represent data sampling and the time when the data is valid.

14             1bit    SPR1    

15             0bit    SPR0

16             

17             

18             

19             

20 SPCR (SPI Status Register)

21 SPDR (SPI Control Register data register)

22     

23 Author’s email: jikexianfeng@outlook.com

24 ********************************/

25 #define SCK_PIN 13 //Macro definition of clock port

26 #define MISO_PIN 12 //Macro definition of host output line

27 #define MOSI_PIN 11 //Macro definition of slave output line

28 #define SS_PIN 10 //Chip select

29 boolean SlaveDataFlag; //Data flag

30 

31 void MasterInit(void) //Initialize SPI pin settings

32 {

33 pinMode(SCK_PIN,OUTPUT); //SCK_PIN is output mode (host mode)

34 pinMode(MOSI_PIN,OUTPUT); //Initialize host output bus

35 pinMode(MISO_PIN,INPUT); //Initialize slave output bus

36 pinMode(SS_PIN,OUTPUT); //Initialize chip select pin (high level for host, low level for slave)

37 //Start SPI

38   SPCR = B00000000;

39   SPCR = (1<40 }

41 

42 byte ReadByte(void)

43 {

44   while(!(SPSR&(1<45   return SPDR;

46 }

47 

48 void WriteByte(byte value)

49 {

50   SPDR = value;

51   while(!(SPSR&(1<52   return ;

53 }

54 

55 void setup()

56 {

57   Serial.begin(115200);

58   MasterInit();

59   Serial.println("jikexianfeng@outlook.com");

60   digitalWrite(SS_PIN,HIGH);

61   

62   SlaveDataFlag = true;

63 }

64 

65 void loop()

66 {

67   byte rxData;

68   while(true)

69   {

70     if(SlaveDataFlag)

71     {

72       digitalWrite(SS_PIN,LOW);

73       WriteByte(17);

74       Serial.println("Done writing data...");

75       Serial.println("Reading data from slave ...");

76       rxData = ReadByte();

77       digitalWrite(SS_PIN,HIGH);

78       Serial.println("Dome Reading data ...");

79       Serial.print("From Slave :");

80       Serial.println(rxData,DEC);

81       SlaveDataFlag = false;

82     } 

83   }

84 }

From the machine:

 1 /*********************************

 2 Code function: Implement SPI data transmission (host side) through the underlying AVR method

 3. Creation time: 2016*10*17

 4. Use resources:

 5 Lower-level aTmega (AVR) library

 6 Author’s email: jikexianfeng@outlook.com

 7 ********************************/

 8 #define SCK_PIN 13

 9 #define MISO_PIN 12

10 #define MOSI_PIN 11

11 #define SS_PIN 10

12 

13 void SlaveInit(void)

14 {

15   pinMode(SCK_PIN,INPUT);

16   pinMode(MISO_PIN,INPUT);

17   pinMode(MISO_PIN,OUTPUT);

18   pinMode(SS_PIN,INPUT);

19   

20   SPCR = B00000000;

21   SPCR = (1<22 }

23 

24 byte ReadByte(void)

25 {

26   while(!(SPSR&(1<27   return SPDR;

28 }

29 

30 void writeByte(byte value)

31 {

32   SPDR = value;

33   while(!(SPSR&(1<34   return ;

35 }

36 

37 void setup()

38 {

39   Serial.begin(115200);

40 SlaveInit();

41 }

42 

43 void loop()

44 {

45   if(digitalRead(SS_PIN) == LOW)

46   {

47     writeByte(19);

48     byte rxData;

49     rxData = ReadByte();

50     Serial.print("Command :");

51     Serial.println(rxData);

52   }

53 }