doubt on digital logic system

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Bhuvanesh Nick

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i seen in it in a page it is mentioned we are using positive logic systems that is above +2v for on and below 0.8 to for off.but in below statement its said to ground for 0 .if i do so it looks like - voltage ..help me plzz

"we can define the ideal Digital Logic Gate as one that has a "LOW" level logic "0" of 0 volts (ground) and a "HIGH" level logic "1" of +5 volts and this can be demonstrated as:"
 

In digital logic, there are two levels 1 and 0 also called as High and low respectively. while implementing in hardware, the designer can set any voltage level to high/low and w.r.t that level, voltage for low/high is set.
In your first sentence, voltages above +2 is considered as logic high and voltage below 0.8 is considered as logic low. Between 2 and 0.8 it is undefined, that is your harware can consider t high or low. we cant say. This voltage level for 1 and 0 is specific to particular tech and design.
In the second statement of yours, they have taken 0V for logic 0 and 5V for logic 1.

In ECL logic you can find logic 1 defined at -0.2V and logic 0 defined as -5V
So different technology/design has different voltage level definition for logic 1 and 0. usually higher voltage is defined for 1 and lower voltage is defined for 0
here reference from wiki
https://en.wikipedia.org/wiki/Logic_level
checkout the voltage levels for different technology.
 

now i am clear with what you say.as there are positive and negative logic system setting on and off.if i connect one input has +5v and other is -5 .what will u consider..a postive logic or a negative logic system
 

its a positive logic system if u assign +5V as logic 1 and -5V as logic 0. If u assign logic 1 for -5V and logic 0 for +5V then it is negative logic system.

- - - Updated - - -

its a positive logic system if u assign +5V as logic 1 and -5V as logic 0. If u assign logic 1 for -5V and logic 0 for +5V then it is negative logic system.

"In ECL logic you can find logic 1 defined at -0.2V and logic 0 defined as -5V " --This is a positive logic system since higher voltage is given to logic 1 and lower voltage to logic 0.
 
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