First you need to know the slave ID of the I2C slave.
Then from the data sheet, find out what addresses you need to write to the sensor (how many bytes) before you can read the data. Then use the I2C_WRITE command followed by I2C_READ command to get the data into the DM area.
I2C_WRITE command does not send a I2C_STOP bit automatically. So a I2C_READ followed by a I2C_WRITE will send a RESTART bit to the I2C slave and the slave will then start to output the data that the master wishes to read.
Attached is a sample program to write to the RTC chip internal RAM data area and then read back some data using the I2C commands.
