Race Conditions

In some situations, the output of a circuit may be unstable. For example,

Here, the output of the NAND gate feeds back into one of its inputs. If we look at the truth table for the NAND gate, it can be seen that an input of 0 and 1, gives us an output of 1. However, when the other input goes logic high, the output will go logic zero. Now we have a problem. The inputs are back to 0 and 1 and so the output once again goes logic high. The output of the NAND gate will never become stable and this is called a race condition.