# Question about diode logic gate

#### The King of Electronics

Joined May 12, 2013
3
Hi everyone,
why we use resister when we design AND/OR-logic gate ?

#### MrChips

Joined Oct 2, 2009
29,865
The resistor R presents a load.
Without R (R = 0) you would destroyed the diodes whenever A or B is connected to GND.

#### The King of Electronics

Joined May 12, 2013
3
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 ?

#### kubeek

Joined Sep 20, 2005
5,791
The diodes would be off and you would have undefined output voltage.

#### BillB3857

Joined Feb 28, 2009
2,569
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?

#### MrChips

Joined Oct 2, 2009
29,865
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.)