1SPS mode of ADT7311

I'm using ADT7311. When using the 1SPS mode, I tried to use the procedure below:

1. Configure it to work in 1SPS mode.
2. Check the nRDY bit in a while loop, when it is '0', then read the temperature data.
3. Check the nRDY bit to wait it to be '1', in a busy loop. When it goes to '1', goto step 2, ........

My problem is, the first conversion is always OK, but then nRDY never went to '1', so I stuck in step 3. However, the doc describe 'nRDY' as below:

This bit goes low when the temperature conversion result is written into the temperature value
register. It is reset to 1 when the temperature value register is read. In one-shot and 1 SPS modes,
this bit is reset after a write to the operation mode bits.

I don't think my usage violated the rules above. So, I think there may be something the doc doesn't explain clearly.

Any help? 

Thanks.