I2C环回模式

Question

这是LM4F120H5QR I2C环回模式的程序，我使用PB2和PB3作为scl和sda。我无法从数据寄存器读取数据，MTPR（SCL CLOCK PERIOD）也从7变为1.

#include<stdio.h>
#include<stdint.h>
#include<lm4f120h5qr.h>
void transmit()
{
    while(I2C0_MASTER_MCS_R & 0x1); // WAIT TILL BUSY BIT IS FREE
    I2C0_MASTER_MSA_R=0x0;         // RS BIT-0 FOR TRANSMIT
    I2C0_MASTER_MDR_R=0x0A;        // WRITING DATA
    I2C0_MASTER_MCS_R =0x03;       //START + RUN BIT ENABLE
    while(I2C0_MASTER_MCS_R & 0x1); //WAIT
    I2C0_MASTER_MCS_R = 0x01;       // ENABLE TRANSMIT
    while(I2C0_MASTER_MCS_R & 0x1); // WAIT
    I2C0_MASTER_MCS_R =0x05;        //STOP
    while(I2C0_MASTER_MCS_R & 0x1); //WAIT
}

int main()
{
    char ch=0;
    SYSCTL_RCC_R = 0x01521540;  // CLOCK                        
    SYSCTL_RCC2_R = 0xC1004000;
    SYSCTL_RCGCI2C_R |= 0x01;    // CLOCK FOR I2C
    SYSCTL_RCGCGPIO_R |=0x02;   //CLOCK FOR GPIO                    
    GPIO_PORTB_DIR_R &= ~0x0C;  // DIRECTION                        
    GPIO_PORTB_AFSEL_R |= 0x0C; //ALTERNATE FUNCTION                        
    GPIO_PORTB_PCTL_R |= 0x3300;    // PORT CONTROL                 
    GPIO_PORTB_DR2R_R |= 0x0C;  // 2 mA                     
    GPIO_PORTB_PUR_R |= 0x0C;    // pull up resistors
    GPIO_PORTB_ODR_R |= 0x08;   // open drain for sda                   
    GPIO_PORTB_DEN_R |= 0x0C;   // digital enable                       
    I2C0_MASTER_MCR_R |= 0x01;  // loopback mode enable                             
    I2C0_MASTER_MTPR_R |= 0x07; // scl clock period 100 kbps                            
    transmit();
    while(I2C0_MASTER_MCS_R & 0x1); // wait             
    I2C0_MASTER_MSA_R =0x0;         // RS bit is 0 to txt clock             
    I2C0_MASTER_MCS_R = 0x03;        // start+run
    while(I2C0_MASTER_MCS_R & 0x1);  //wait
    I2C0_MASTER_MCS_R = 0x05;        //stop
    while(I2C0_MASTER_MCS_R & 0x1);  // wait
    I2C0_MASTER_MSA_R |=0x1;         //RS bit 1 to receive
    I2C0_MASTER_MCS_R= 0x0B;         // ack+start+run
    while(I2C0_MASTER_MCS_R & 0x1);  //wait
    ch=I2C0_MASTER_MDR_R;            //reading the data
    while(I2C0_MASTER_MCS_R & 0x1);  // wait
    I2C0_MASTER_MCS_R=0x05;          //stop
    while(I2C0_MASTER_MCS_R & 0x1);  //wait
}