A digital signal is a discrete signal with out time of discrete values is called as digital signal it has 2 discrete values or levels. The values can be represented by using the terms low & high The 2 different represents of digital signals are

1. Positive Logic Signal

2. Negative Logic Signal

$\underline{POSITIVE \ LOGIC \ SIGNAL}$:- For the 5V if the signal is +ve logic signal then for the voltage in the range of 3.5v to 5v will be considered as High level & the original voltage/current in the range of 0 to 1 will be considered as low level fig 1.shown +ve logic signal this high & low level range will be different for the different I/P signals

$\underline{NEGATIVE \ LOGIC \ SIGNAL}$:-For the 5v Digital input signal if the signal is negative logic signal the for the voltage/current in the range of 3 to 5 will be considered as high level fig 2. shown Negative logic signal. It is just opposite of positive logic signal

The 2 levels high & low can be represented by the binary digits 0 & 1 & 0 respectively the binary (bie=two) number system & are referred as binary digits or bits