LTC6948-2 unlock

 i use register as follow,but it does not lock , the ref is 40M,pfd is 20M  output frequency is 985M,integer mode , how can slove this problem

LTC6948_write(0x01,0x04); 
LTC6948_write(0x02,0x0c); 
LTC6948_write(0x03,0Xbd); 
LTC6948_write(0x04,0X28); 
LTC6948_write(0x05,0X00); 
LTC6948_write(0x06,0X10); 
LTC6948_write(0x07,0Xc5); 
LTC6948_write(0x08,0X00); 
LTC6948_write(0x09,0X00); 
LTC6948_write(0x0a,0X00); 
LTC6948_write(0x0b,0Xbc); 
LTC6948_write(0x0c,0X4f); 
LTC6948_write(0x0d,0Xe4);