TLC5955 GSCLK and LAT signal

Hello,

We are using the TLC5955, but the data sheet is lacking some information on its operation, and we have a few questions.

1. Does the GSCLK have to be running constantly to keep the LED’s illuminated? Or is the GSCLK line only important for writing data to the chips.
2. The only way we have been able to illuminate any LED’s is to free run the GSCLK on startup which initializes whatever random defaults the chip has upon start up.
3. Is it required to write any data to the chips twice BEFORE triggering the LAT signal? Or are we supposed to only write once for each LAT signal. 

Thank you