通过MAX2990 I2C接口向标准EEPROM (24C04)连接的方法
时间:02-21
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引言
本文介绍了如何通过MAX2990电力线通信调制解调器的I2C接口与外部EEPROM 24C04连接,并给出了相应的固件例程。I²C总线受控于MAX2990 (主机),24C04 EEPROM为从机器件。以下框图给出了本文示例的硬件配置。
![](../img/eep/emb/emb-20779puraaodmtfy.jpg)
固件说明
I²C接口初始化
一旦使能I²C模块,SCL和SDA必须配置成漏极开路状态,以确保I²C总线通信正常。由于I²C是GPIO端口的一个替代功能,固件必须确保SCL和SDA输入在初始化期间禁止上拉(通过对端口控制器的输出位写零实现)。
示例中,时钟频率为250kHz。首先需要配置MAX2990的I²C接口:
PO1_bit.Bit2 = 0; // Disables the GPIO function of thePO1_bit.Bit3 = 0; // I2C pinsI2CCN_bit.I2CEN = 0; // Makes sure that I2C is disabled// to allow the changing of the I2C settingsI2CCN_bit.I2CMST = 1; // Sets the I2C engine to master modeI2CCN_bit.I2CEA = 0; // 7-bit address modeI2CCK_bit.I2CCKL = 0x40; // 2µs CLK-low, to define I2C frequencyI2CCK_bit.I2CCKH = 0x40; // 2µs CLK-high, to define I2C frequencyI2CTO = 200; // I2C_TIMEOUTI2CST = 0x400; // Resets I2C status registerI2CCN_bit.I2CEN = 1; // Enables the I2C engine
写模式
写入24C04 EEPROM时,必须通过I²C接口写入以下字节:
- EEPROM的I²C总线地址(这里为0xA0)
- EEPROM存储器的地址
- 数据字节(地址将自动递增)
示例中试图写入以下字节,从0x00地址开始,向EEPROM写入:0x12、0x34、0x56、0x78和0x90。
i2c_init_write(); // Sets the MAX2990 I2C Engine into write modei2c_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// automaticallyi2c_write(0x00); // word address locationi2c_write(0x12); // data1i2c_write(0x34); // data2i2c_write(0x56); // data3i2c_write(0x78); // data4i2c_write(0x90); // data5I2C_STOP; // Sends I2C stop-condition
读模式
读取我们写入EEPROM的数据时,为24C04留出足够的写时间非常关键。通常在“停止条件”后留出几个毫秒的时间,请参考数据资料,确认您的时间设置符合IC的要求。
i2c_init_write(); // Sets the MAX2990 I2C engine into write modei2c_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// automaticallyi2c_write(0x00); // word address locationi2c_init_read(); // Sets the MAX2990 I2C engine into read modei2c_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// automaticallyunsigned char data[5]; // Array to store the received datai2c_read(data[0]); // Reads 1 byte from I2C and writes it to the arrayi2c_read(data[1]); // Reads 1 byte from I2C and writes it to the arrayi2c_read(data[2]); // Reads 1 byte from I2C and writes it to the arrayi2c_read(data[3]); // Reads 1 byte from I2C and writes it to the arrayi2c_read(data[4]); // Reads 1 byte from I2C and writes it to the arrayI2C_STOP; // Sends I2C stop-condition现在,我们可以验证一下用于EEPROM读、写操作的功能。
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 modeI2CCN_bit.I2CACK = 1; // Creates I2C NACK so that slave can create ACKI2C_START; // Generates I2C START conditionwhile( I2CCN_bit.I2CSTART == 1 ); // Waits until the START condition// was put to the I2C busI2CST_bit.I2CSRI = 0; // Resets the I2C interrupt flag}int i2c_init_read(void){I2CCN_bit.I2CMODE = 1; // I2C read-modeI2CCN_bit.I2CACK = 0; // Creates I2C ACK after receiveI2C_START; // Generates I2C START conditionwhile( I2CCN_bit.I2CSTART == 1 ); // Waits until the START conditionI2CST_bit.I2CSRI = 0; // Resets the I2C interrupt flag}void i2c_write(UINT8 data){I2CBUF = data; // Puts the data on the I2C buswhile( I2CST_bit.I2CTXI == 0 ); // Waits for transfer completeI2CST_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 zeroswhile( !I2CST_bit.I2CRXI ); // Waits for receive completeI2CST_bit.I2CRXI=0; // Resets the I2C receive complete// interrupt flag*data = I2CBUF; // Writes the data to the pointer}
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