IIC
IIC总线中断发生在：当完成了1字节发送或者接收操作。
最近在看IIC总线，想了解一下其工作的原理是什么，以2440芯片为例，看了一下IIC的例程，基本了解了主机的发送以及接收。
2440作为主机，24C04（EEPROM）作为从机，用的是中断方式发送字节，不是轮询。
以下是我的一些分析：
1.先将主函数贴出如下：
void Main(void)
{
memcpy((unsigned char *)0x0,(unsigned char *)0x30000000,0x1000);//复制到内存
SetSysFclk(FCLK_400M); //设置系统时钟 400M
ChangeClockDivider(2, 1); //设置分频 1：4：8
CalcBusClk(); //计算总线频
Uart_Select(0);
Uart_Init(0, 115200); //选择uart0，波特率为115200来打印一些显示的信息。
Test_Iic();
// Test_Iic2();
while(1);
}
主要的是对Test_iiC()函数的分析：
void Test_Iic(void)
{
unsigned int i,j,save_E,save_PE; //定义4个无符号整形变量
static U8 data[256]; //定义一个256的数组
Uart_Printf("[ IIC Test(Interrupt) using AT24C04 ]\n"); //串口打印[ IIC Test(Interrupt) using AT24C04 ]\n
save_E = rGPECON;
save_PE = rGPEUP; //配置GPIO的E端口为上拉
rGPEUP |= 0xc000; //Pull-up disable
rGPECON |= 0xa0000000; //GPE15:IICSDA , GPE14:IICSCL ，配置IIC的引脚
pISR_IIC = (unsigned)IicInt; //中断函数，清除中断挂起
rINTMSK &= ~(BIT_IIC); //正常IIC的中断服务程序
//Enable ACK, Prescaler IICCLK=PCLK/16, Enable interrupt, Transmit clock value Tx clock=IICCLK/16
// If PCLK 50.7MHz, IICCLK = 3.17MHz, Tx Clock = 0.198MHz
rIICCON = (1<<7) | (0<<6) | (1<<5) | (0xf);
rIICADD = 0x10; //2440 slave address = [7:1]，这是主机的IIC地址
rIICSTAT = 0x10; //IIC bus data output enable(Rx/Tx)，设置IIC宗信啊输出数据使能。
rIICLC = (1<<2)|(1); // Filter enable, 15 clocks SDA output delay added by junon
Uart_Printf("Write test data into AT24C04\n"); //在uart0输出Write test data into AT24C04\n
for(i=0;i<256;i++)
Wr24C04(0xa0,(U8)i,i); //这是具体给24C04写字节的函数，0xa0是从机的地址，（U8）i是往23c04的写数据的地址，i是数据
void Wr24C04(U32 slvAddr,U32 addr,U8 data) //Wr24C04(0xa0,(U8)i,i);
{
_iicMode = WRDATA; //IIC
的工作模式
_iicPt = 0; //对发送的数组个数进行计数
_iicData[0] = (U8)addr; //发送的地址
_iicData[1] = data; //要发送的数组定义
_iicDataCount = 2; //初始化发送的字节数为2
rIICDS = slvAddr; //0xa0 ，从机的地址
rIICSTAT = 0xf0; //MasTx,Start，开始发送
//Clearing the pending bit isn't needed because the pending bit has been cleared.
//当发送完一个字节从这里跳到中断中执行。
void __irq IicInt(void) //中断处理函数
{
U32 iicSt,i;
rSRCPND = BIT_IIC; //Clear pending bit,源挂起寄存器，清除原挂起寄存器
rINTPND = BIT_IIC; //中断挂起寄存器，清除中断挂起寄存器
iicSt = rIICSTAT; //IIC总线控制状态寄存器
if(iicSt & 0x8){} //When bus arbitration is failed.
if(iicSt & 0x4){} //When a slave address is matched with IICADD
if(iicSt & 0x2){} //When a slave address is 0000000b
if(iicSt & 0x1){} //When ACK isn't received
//当出现以上四种情况时，该如何处理。
switch(_iicMode)
{
case POLLACK:
_iicStatus = iicSt; //转换到IIC最开始的状态
break;
case RDDATA: //读数据
if((_iicDataCount--)==0)
{
_iicData[_iicPt++] = rIICDS;
rIICSTAT = 0x90; //Stop MasRx condition
rIICCON = 0xaf; //Resumes IIC operation.
Delay(1); //Wait until stop condtion is in effect.
//Too long time...
//The pending bit will not be set after issuing stop condition.
break;
}
_iicData[_iicPt++] = rIICDS; //The last data has to be read with no ack.
if((_iicDataCount)==0)
rIICCON = 0x2f; //Resumes IIC operation with NOACK.
else
rIICCON = 0xaf; //Resumes IIC operation with ACK
break;
case WRDATA: //写数据
if((_iicDataCount--)==0)
{
rIICSTAT = 0xd0; //Stop MasTx condition
rIICCON = 0xaf; //Resumes IIC operation.
Delay(1); //Wait until stop condtion is in effect.等到停止条件生效
//The pending bit will not be set after issuing stop condition.
break; //发出停止条件后，将不会设置挂起位，其实挂起是硬件自动设置的。
}
rIICDS = _iicData[_iicPt++]; //_iicData[0] has dummy.
for(i=0;i<10;i++); //for setup time until rising edge of IICSCL，IICSCL的上升沿开始。
rIICCON = 0xaf; //resumes IIC operation.恢复IIC操作，接着发送下一字节数据
break;
case SETRDADDR:
// Uart_Printf("[ S%d ]",_iicDataCount);
if((_iicDataCount--)==0)
break; //IIC operation is stopped because of IICCON[4]
rIICDS = _iicData[_iicPt++];
for(i=0;i<10;i++); //For setup time until rising edge of IICSCL
rIICCON = 0xaf; //Resumes IIC operation.
break;
default:
break;
}
}
while(_iicDataCount!=-1); //当没有发送完时，一直在这里等待。
_iicMode = POLLACK; //轮询ACk
//下面这个while(1)其实只能检测发送数据的应答位
while(1)
{
rIICDS = slvAddr; //给移位寄存器赋值为从机地址
_iicStatus = 0x100;
rIICSTAT = 0xf0; //MasTx,Start
rIICCON = 0xaf; //Resumes IIC operation.
//从这里跳入中断
while(_iicStatus==0x100);
if(!(_iicStatus&0x1))
break; //When ACK is received，当ACk==1,则跳出循环。
}
rIICSTAT = 0xd0; //Stop MasTx condition，停止发送。
rIICCON = 0xaf; //Resumes IIC operation. 复位IIC的操作
Delay(1); //Wait until stop condtion is in effect.
//Write is completed.
}
for(i=0;i<256;i++)
data[i] = 0;
Uart_Printf("Read test data from AT24C04\n");
for(i=0;i<256;i++)
Rd24C04(0xa0,(U8)i,&(data[i]));
void Rd24C04(U32 slvAddr,U32 addr,U8 *data) //从机地址，地址，数据,Rd24C04(0xa0,(U8)i,&(data[i]));
{
_iicMode = SETRDADDR; //设置读的地址
_iicPt = 0;
_iicData[0] = (U8)addr;
_iicDataCount = 1;
rIICDS = slvAddr;
rIICSTAT = 0xf0; //MasTx,Start
//Clearing the pending bit isn't needed because the pending bit has been cleared.
while(_iicDataCount!=-1);
_iicMode = RDDATA;
_iicPt = 0;
_iicDataCount = 1;
rIICDS = slvAddr;
rIICSTAT = 0xb0; //MasRx,Start
rIICCON = 0xaf; //Resumes IIC operation.
while(_iicDataCount!=-1);
*data = _iicData[1];
}
//Line changed 0 ~ f
for(i=0;i<16;i++)
{
for(j=0;j<16;j++)
Uart_Printf("%2x ",data[i*16+j]);
Uart_Printf("\n");
}
rINTMSK |= BIT_IIC;
rGPEUP = save_PE;
rGPECON = save_E;
}
以上是主机发送和接收的例子，其工作原理其实很简单，如下图所示：
由起始位开始，发送从机的7位地址，第八位是读写方式，之后数据传输方式是数据+ACK位，ACK位是由从机响应的，也就是时钟的第9个周期响应，在第 九个周期内，主机的数据输出位保持为高电平，从机的数据接收位保持为低电平。这个ACK位是由硬件操作的，无需软件控制，每发送一个字节的数据，都会接收到一个响应位。p是停止位。
下图是ACK发生时的电位图：
主机处于发送模式的流程图如下：
当主机处于接收模式时，如下图所示：
黑色显示的是从从机到主机传输，白色显示的是从从主机到从机传输。
其工作流程如下图所示：
posted on 2018-10-04 18:48 xiegangqingnian 阅读(429) 评论(0) 编辑 收藏 举报
