# What is the maximum capacitance allowed on SMBus? Why was the VIL fixed to a maximum of 0.8V?

How to interpret the significance of DC specification in SMBus? Why is the VIH value has been fixed to a minimum of 2.1V?

• Suppose I write a specification about my bus: RBbus. I specify that $V_{IL} < 0.7 V$. Then you make a design with the RBbus I specified but you use components that are specified for $V_{IL} < 0.9 V$ so $V_{IL} = 0.8 V$ would work OK (you need that for some reason). It works fine but it violates my RBbus spec. so you cannot and should not call it RBbus. As a user of SMBus you do not need to know why a spec. is < 0.8 V, you only need to follow it. – Bimpelrekkie Aug 12 '20 at 13:41
• I agree with you Bimpelrekkie, but I just wanted to know that If I2C was already defined and I2C specifies VIH/VIL based on VDD i.e 0.7*VDD/0.3*VDD then what made them go back to defining a fixed level for VIH/VIL. – Govind Srivastav Aug 12 '20 at 14:20