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

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    \$\begingroup\$ 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. \$\endgroup\$ Aug 12 '20 at 13:41
  • \$\begingroup\$ 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. \$\endgroup\$ Aug 12 '20 at 14:20
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read SMBus 1.1 specifications which has very vague details on the Vih,Vil dependency on Vcc.

It doesn't explain full details but given one para of explanation. I can't put this image into comment, otherwise i could have given comment itself instead of answer. This is not actual answer.

enter image description here

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  • \$\begingroup\$ Thanks!! Now it is clear. \$\endgroup\$ Aug 12 '20 at 14:55
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Why is the VIH value has been fixed to a minimum of 2.1V?

It sounds like it's to make it somewhat compatible with TTL logic levels: -

enter image description here

But, as per what Bimpelrekkie says in his comment, (paraphrased) it is what it is.

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