I2C Protocol Fast Mode

[smashash147]

Hi all,
Going through the I2C spec. I came across the fact that :-

"The inputs of Fast-mode devices incorporate spike
suppression and a Schmitt trigger at the SDA and SCL
input."


What is the role of schmitt trigger here??

 

[pico]

Schmitt trigger - Wikipedia, the free encyclopedia

 

[smashash147]

Iam quite clear with what a schmitt trigger is but wrt to the I2C protocol how does it help in the Fast Mode operation ..??????

 

[karthikkrv85]

Hi all,
Going through the I2C spec. I came across the fact that :-

"The inputs of Fast-mode devices incorporate spike
suppression and a Schmitt trigger at the SDA and SCL
input."


What is the role of schmitt trigger here??

Hai i think the schmitt trigger circuit at the fast mode slave or master devices are going to help the controller to recognize the logical levels of the signal. I mean the schmitt trigger circuit is going to act like reshaping the signal

I am not sure whether it is correct or not.

Thanks

 

[shaiko]

smashash147,

The schmitt trigger on the inputs serves only one purpose:
Noise immunity.
We add certainty that if an input is at '1' or '0' volts - it's the correct voltage level and not due to noise.
You see, noise can cause a voltage level change at the Rx end and appear to be different than what the Tx is sending.
BUT, this effect is very short termed! By adding the trigger, the circuit becomes more immune to noise...

Think of the following example:
An elevetor button has been purely designed and gets pushed by the slightest touch or maybe even a breeze of wind (noise).
If we add a trigger we make sure that it takes more time to push the button to call the elavator - a human finger can call it with a long intentional press, while the wind cannot.

 

[smashash147]

Thanks shaiko that was a very enlighting explanation...