Are digital inputs of data acquisition devices differential or single ended?
There will be no single/differential end digital i/o 's


single end: Measure the voltage between the input signal and analog ground.
differential end: measure the voltage between two distinct input signals.


digital inputs will be either HIGH/LOW with respect to Ground

CM noise rejection:
actually lets say there is a bridge sensor. The sensor measurement of ADC is independent of the low level ground which makes it more free of noise. The reason for this is that the noise source is present on both signal leads and when in differential mode only the difference between the two leads is measured.

Regarding your both the images 

first image is differential ended analog input 

second one is single ended analog input 

if a digital signal heve noise lets say, but 


it will receive that data as 



since usually in most of 

TTL cirucits

0 to 0.8V - LOW

2 V to VCC - LOW

if in cmos

0 to 1/3VCC - LOW

2/3 to VCC - HIGH

there is a lot of width b/w LOW and HIGH