如何使用MAX2990 I²C接口编写工业标准EEPROM

文章和固件代码示例介绍了如何使用MAX2990电力线通信调制解调器上的IC接口与外部EEPROM 24C04接口。

介绍

本应用笔记和固件代码示例描述了MAX2990电力线通信调制解调器上的IC接口如何与外部EEPROM 24C04接口。IC总线由MAX2990（主机）控制，24C04 EEPROM由从机控制。下面的示意图显示了此示例中使用的硬件配置。

固件说明

IC接口初始化

每当使能IC模块时，SCL和SDA必须配置为漏极开路。此配置是IC通信正常运行所必需的。由于IC是GPIO端口的替代功能，固件必须确保在初始化期间禁用SCL和SDA输入上的上拉（通过将零写入该端口控制器输出位）。

该示例具有 250kHz 时钟频率。首先，需要在MAX2990中设置IC接口，如下所示：

PO1_bit.Bit2 = 0; 		// Disables the GPIO function of the
PO1_bit.Bit3 = 0; 		// I2C pins

I2CCN_bit.I2CEN = 0; 	// Makes sure that I2C is disabled
			// to allow the changing of the I2C settings

I2CCN_bit.I2CMST = 1; 		// Sets the I2C engine to master mode
I2CCN_bit.I2CEA = 0; 		// 7-bit address mode
I2CCK_bit.I2CCKL = 0x40; 	// 2µs CLK-low, to define I2C frequency
I2CCK_bit.I2CCKH = 0x40; 	// 2µs CLK-high, to define I2C frequency

I2CTO = 200; 		// I2C_TIMEOUT
I2CST = 0x400; 		// Resets I2C status register

I2CCN_bit.I2CEN = 1; 		// Enables the I2C engine

写入模式

要写入 24C04 EEPROM，必须通过 IC 接口写入以下字节：

IC EEPROM 的地址（在本例中0xA0）

EEPROM 中存储器位置的地址

数据字节（地址将自动增加）

在此示例中，我们尝试从位置0x00开始将以下字节写入EEPROM：0x12，0x34，0x56，0x78和0x90。

i2c_init_write(); 	// Sets the MAX2990 I2C Engine into write mode
i2c_write(0x50); 	// 24C04 write (adr = 0b1010 000 0) = 0xA0
			// The MAX2990 I2C engine shifts the I2C address by
			// 1 bit, because it will generate the R/W bit
			// automatically

i2c_write(0x00); 	// word address location
i2c_write(0x12); 	// data1
i2c_write(0x34); 	// data2
i2c_write(0x56); 	// data3
i2c_write(0x78); 	// data4
i2c_write(0x90); 	// data5
I2C_STOP; 		// Sends I2C stop-condition

阅读模式

为了回读数据，我们从EEPROM写入。重要的是，我们要给 24C04 足够的时间来编写。这通常需要在“停止条件”后的几毫秒内。请查阅IC的数据手册，确保使用正确的时序。

i2c_init_write(); 	// Sets the MAX2990 I2C engine into write mode
i2c_write(0x50); 	// 24C04 write (adr = 0b1010 000 0) = 0xA0
			// The MAX2990 I2C engine shifts the I2C address by
			// 1 bit, because it will generate the R/W bit
			// automatically

i2c_write(0x00); 	// word address location

i2c_init_read(); 	// Sets the MAX2990 I2C engine into read mode

i2c_write(0x50); 	// 24C04 read (adr = 0b1010 000 1) = 0xA1
			// The MAX2990 I2C engine shifts the I2C address by
			// 1 bit, because it will generate the R/W bit
			// automatically

unsigned char data[5]; 		// Array to store the received data
i2c_read(data[0]); 		// Reads 1 byte from I2C and writes it to the array
i2c_read(data[1]); 		// Reads 1 byte from I2C and writes it to the array
i2c_read(data[2]); 		// Reads 1 byte from I2C and writes it to the array
i2c_read(data[3]); 		// Reads 1 byte from I2C and writes it to the array
i2c_read(data[4]); 		// Reads 1 byte from I2C and writes it to the array
I2C_STOP; 			// Sends I2C stop-condition

现在我们检查以下用于读取和写入EEPROM的函数。

i2c_init_write(void)
i2c_init_read(void)
i2c_write(UINT8 data)
i2c_read(UINT8 *data)

void i2c_init_write(void)
{
I2CCN_bit.I2CMODE = 0; 	// I2C transmit mode
I2CCN_bit.I2CACK = 1; 	// Creates I2C NACK so that slave can create ACK
I2C_START; 		// Generates I2C START condition
while( I2CCN_bit.I2CSTART == 1 ); 	// Waits until the START condition
					// was put to the I2C bus
I2CST_bit.I2CSRI = 0; 			// Resets the I2C interrupt flag
}

int i2c_init_read(void)
{
I2CCN_bit.I2CMODE = 1; 	// I2C read-mode
I2CCN_bit.I2CACK = 0; 	// Creates I2C ACK after receive
I2C_START; 		// Generates I2C START condition

while( I2CCN_bit.I2CSTART == 1 ); 	// Waits until the START condition
I2CST_bit.I2CSRI = 0; 			// Resets the I2C interrupt flag
}

void i2c_write(UINT8 data)
{
I2CBUF = data; 				// Puts the data on the I2C bus
while( I2CST_bit.I2CTXI == 0 ); 	// Waits for transfer complete
I2CST_bit.I2CTXI = 0; 			// Resets the I2C transmit complete
					// interrupt flag
}

void i2c_read(UINT8 *data)
{
I2CBUF = 0xff; 		// Puts "all ones" on the I2C bus so that slave can pull
			// the bus down to generate zeros

while( !I2CST_bit.I2CRXI ); 		// Waits for receive complete
I2CST_bit.I2CRXI=0; 			// Resets the I2C receive complete
					// interrupt flag

*data = I2CBUF; 			// Writes the data to the pointer
}

审核编辑：郭婷