LM3S9B92 I2C not work

The following codes doesn't work, don't know why?
please point out the faults, thanks.

***********************************************
SysCtlPeripheralEnable(SYSCTL_PERIPH_I2C0);
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
I2CMasterInitExpClk(I2C0_MASTER_BASE, SysCtlClockGet();, true);
GPIOPinTypeI2C(GPIO_PORTB_BASE, GPIO_PIN_2 | GPIO_PIN_3 );
I2CMasterEnable(I2C0_MASTER_BASE);
while(1)
{ while(I2CMasterBusBusy(I2C0_MASTER_BASE)) ; I2CMasterDataPut(I2C0_MASTER_BASE, 'U');
} *************************************************

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