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MSP430F5529 IIC初始化后已启动IIC传输,IIC clock没有时钟输出

试了UCB0,UCB1的IIC都是一样的请款,一旦启动IIC传输,IIC clock就变为低电平,没有时钟输出。

IIC初始化代码如下:

P4SEL |= 0x06; // Assign I2C pins to USCI_B0
UCB1CTL1 |= UCSWRST; // Enable SW reset
UCB1CTL0 = UCMST + UCMODE_3 + UCSYNC; // I2C Master, synchronous mode
UCB1CTL1 = UCSSEL_2 + UCSWRST+UCTR; // Use SMCLK
UCB1BR0 = 12; // fSCL = SMCLK/12 = ~100kHz
UCB1BR1 = 0;
UCB1I2CSA = 0x48; // Slave Address is 048h
UCB1CTL1 &= ~UCSWRST; // Clear SW reset, resume operation
UCB1IE |= UCTXIE+UCRXIE+UCSTPIE;
__delay_cycles(SYSTEM_CLOCK_SPEED * 0.05);//delay 50ms

UCB1CTL |= UCTR+UCTXSTT;//启动IIC 传输,IIC clock由高电平立即变为低电平,IIC data保持高电平不变。

请教大侠们!