ADS1216: I can't get the full digital output range, i.e. UNIPOLAR & 0 to 5V

See below my settings:

1. REFEN = 1 (internal ref)
2. REF HI = 1 (2.5V)
3. BUFEN = 0 (disable, need maximum input voltage)
4. My gain is still as default = 000, G=1
5. PSEL = 0000 (channel 0 positive)
6. NSEL = 1000 (AINCOM negative)
7. set BUFEN pin = 0 (disable)
8. U/B data format = 1 )Unipolar)
9. AVDD = 5V, DVDD = 3.3V, analog input signal expected o to 5V respect to Aincom

My digital output:

1. Analog input = 0V ==> digital out put = 000000h
2. Analog input = 2.5V ==> digital out put = FFFFFFh

Any suggestions?

Thank you for your help

Fausto Bartra