How to drive tie hi/lo pins? Why we need tie hi/lo cell?

[zhwa0013]

How to drive tie hi/lo pins? Why we need tie hi/lo cell? What's the difference between a clock tree and the tie hi/lo tree?

 

[mail4idle2]

There is no comparision between ti hi/lo and clock tree.
Clock tree is expansion of clock.

Driving ti hi/lo cells : It does not need any inputs. it gives output high and low depending on tie high and tie low cell respectively.

 

[rca]

The fanout of tie cells are usually controllable.
Some ERC rules would not have direct vdd or vss connected to std cell inputs.