51学习笔记之以硬件spi与max6675通信实现K型热电偶测温

硬件：max6675  STC12C5A60S2 K型热电偶

功能：实现读取K型热电偶温度，并通过上位机打印出实际温度

难点：读取Max6675的数据是16位，而STC12系列单片机每次接收的数据为8位，如何通过硬件SPI实现直接读取Max6675的温度成为一难点。网上相关教程以及相关论文均是采用软件SPI模拟时序方式采集数据，故而通过STC12系列单片机自带的硬件SPI实现直接读取Max6675的数据具有实际研究意义。

代码：

#include "reg51.h"
#include "stdio.h"
#include<intrins.h>           //??_nop_()????
#define MASTER //define:master undefine:slave
#define FOSC 11059200L
#define BAUD (256 - FOSC / 32 / 9600)  //253
typedef unsigned char BYTE;
typedef unsigned int WORD;
typedef unsigned long DWORD;
sfr AUXR = 0x8e; //Auxiliary register
sfr SPSTAT = 0xcd; //SPI status register
#define SPIF 0x80 //SPSTAT.7
#define WCOL 0x40 //SPSTAT.6
sfr SPCTL = 0xce; //SPI control register
#define SSIG 0x80 //SPCTL.7
#define SPEN 0x40 //SPCTL.6
#define DORD 0x20 //SPCTL.5
#define MSTR 0x10 //SPCTL.4
#define CPOL 0x08 //SPCTL.3
#define CPHA 0x04 //SPCTL.2
#define SPDHH 0x00 //CPU_CLK/4
#define SPDH 0x01 //CPU_CLK/16
#define SPDL 0x02 //CPU_CLK/64
#define SPDLL 0x03 //CPU_CLK/128
sfr SPDAT = 0xcf; //SPI data register
sbit SPISS = P1^3; //SPI slave select, connect to slave‘ SS(P1.4) pin
void InitUart();
void InitSPI();
void SendUart(BYTE dat); //send data to PC
BYTE RecvUart(); //receive data from PC
unsigned int SPISwap(); //swap SPI data between master

void Delay_xms(unsigned int z){
    unsigned char i, j;
    unsigned int k;
    for(k=0;k<z;k++){            //for???????1ms??
        _nop_();
        _nop_();
        i = 12;
        j = 84;
        do{while (--j);}
        while (--i);
    }

}

///////////////////////////////////////////////////////////
void main()
{
    unsigned int t;
    unsigned int a= 0x01;
    unsigned int MAX6675_Temp;
    unsigned char Flag_connect;
    InitUart(); //initial UART
    InitSPI(); //initial SPI
    while (1)
    {

//        #ifdef MASTER //for master (receive UART data from PC and send it to slave,
//        // in the meantime receive SPI data from slave and send it to PC)
//        SendUart(SPISwap(RecvUart()));
//        #else //for salve (receive SPI data from master and
//        ACC = SPISwap(ACC); // send previous SPI data to master)
//        printf("dd");
//        #endif
        t=SPISwap();

    Flag_connect=t&0x04;             //?á3?êy?Yμ?D2??ê?èèμ???μ???±ê????￡??????a1±íê?μ???￡??????a0±íê?á??ó
  Flag_connect=Flag_connect>>2;     //MAX6675ê?·??ú??
    t = t<<1;                           //?á3?à′μ?êy?Yμ?D3~D14ê????è?μ
    t = t>>4;
    MAX6675_Temp = t/4-28;                //2aμ?μ????èμ￥??ê?0.25￡??ùò?òa3?ò?0.25￡¨?′3yò?4￡?2??üμ?μ?ò??è?aμ￥??μ????è?μ
    if(Flag_connect==0)       //Flag_connect?a0±íê?èèμ???ò?á??ó￡??aê±??ê????è
    {
        printf("%d\n",MAX6675_Temp);
    }
    else
    {
        printf("?′á?é?\n");
    } 

//        printf("%d\n",t);
////        printf("%d \n",t/4);
        Delay_xms(1000);

    }
}
///////////////////////////////////////////////////////////
void InitUart()
{
    SCON = 0x5a; //set UART mode as 8-bit variable baudrate
    TMOD = 0x20; //timer1 as 8-bit auto reload mode
    AUXR = 0x40; //timer1 work at 1T mode
    TH1 = TL1 = BAUD; //115200 bps
    TR1 = 1;
}
///////////////////////////////////////////////////////////
void InitSPI()
{
    SPDAT = 0; //initial SPI data
    SPSTAT = SPIF | WCOL; //clear SPI status
    #ifdef MASTER
    SPCTL = SPEN | MSTR; //master mode
    #else
    SPCTL = SPEN; //slave mode
    #endif
}

///////////////////////////////////////////////////////////
void SendUart(BYTE dat)
{
    while (!TI); //wait pre-data sent
    TI = 0; //clear TI flag
    SBUF = dat; //send current data
}
///////////////////////////////////////////////////////////
BYTE RecvUart()
{
    while (!RI); //wait receive complete
    RI = 0; //clear RI flag
    return SBUF; //return receive data
}
///////////////////////////////////////////////////////////
unsigned int SPISwap()
{
    unsigned int temp=0;

    SPISS = 0; //pull low slave SS

    SPDAT = 25; //trigger SPI send
    while (!(SPSTAT & SPIF)); //wait send complete
        SPSTAT = SPIF | WCOL; //clear SPI statusa
    temp = SPDAT;
    temp = temp << 8;

    SPDAT = 45;
    while (!(SPSTAT & SPIF)); //wait send complet
    temp = temp | SPDAT;
    SPSTAT = SPIF | WCOL; //clear SPI status

    SPISS = 1; //push high slave SS

    return temp; //return received SPI data
}