Hi Mohit,

the 74** devices are available as LS, HC and HCT.
The 80** and 82** are former NMOS, but now often CMOS.

Most NMOS accept TTL level on its inputs and can drive one TTL load on its outputs.
Some CMOS accept TTL level, but some others not.

Also same devices from different manufacturers can have different input or output levels.

Also different pins on a device can have different input or output levels.

To drive HC from LS or NMOS you need pull up resistors.


Sounds really confusing ?
Yes, no common rule exist !
So you must compare the data sheets of every device, which you want to use.


Peter