What does wired-AND mean in I2C interface?

[brunokasimin]

this term is common in i2c interface.What does this mean?

thx in advanced

 

[srhoar]

Re: wired-AND

In a wired-and, a resistor is tied to VCC. The output is the bottom of the resistor. It will normally be high. But if you connect a transistor to the resistor and ground, and activate it, the output will go low. Now, just keep adding transistors. See image below.

This is why outputs are specified open-collector, so they can be hooked up this way. All have to turn off to for the output to be high.

Red

 

[brunokasimin]

Re: wired-AND

hello srhoar,

that means, whenever one transistor is off but the other are not off, the bottom of the resistor is automatically high??

thx

 

[laktronics]

Re: wired-AND

Hi,
Not so, only when all transistors are off,( all inputs Zero), will the output be high. Functionally it is not 'AND', but wired 'NOR'.
Regards,
Laktronics

 

[A.Anand Srinivasan]

wired-AND

wired AND is a connection method in which the output of two AND gates is connected together directly and this connection acts like a AND gate.... for details see morris mano - digital design... this works only in the case of open collector type digital circuits because when the output of the two AND gates are different one of them has to be forced to zero...