Hi everyone,
why we use resister when we design AND/OR-logic gate ?

 

The resistor R presents a load.
Without R (R = 0) you would destroyed the diodes whenever A or B is connected to GND.

 

The resistor R presents a load.
Without R (R = 0) you would destroyed the diodes whenever A or B is connected to GND.

This happen when we replace R with short circuit, what about replace R with open circuit ?

 

The diodes would be off and you would have undefined output voltage.

 

If you were to draw a truth table of the gate you show, and use Vcc to represent a logic 1 and zero volts to represent logic 0, it will become clear. Now, take the two diodes and turn them around and instead of having the other end of the resistor tied to Vcc, tie it to ground. What do you wind up with in that configuration?

 

Then the circuit will not work on its own but will rely on the load that it is connected to.

(gees, I hate dangling prepositions.)