TLC59208F: The led driver doesnot give the correct period

Part Number: TLC59208F

Hi,
As given in the reference manual to obtain a global blinking period of 1000 milli seconds the GRPFREQ – Group Frequency Register has to be filled with the value 23.

But with the value 23 the global blinking period achieved is almost 960 - 980 milli seconds.
Kindly help.