Two-complement value from ADC, Spartan-3A, 3E

Hi:


I am testing a code for the Analog-to-Digital Converter that has the
Spartan-3A FPGA Starter Kit (LTC1407A-1). The converted value from the
ADC is displayed on the LCD.

Without sending voltage input to the VINA (Channel 0), when I command
the ADC to take a sample of the channel, I get the 11111111111111
value as the digital value that the ADC converted.

-->> Is it normal to get that value, when the ADC samples the channel
and when I have not sent any voltage to that pin/channel?



Thanks,
m