The image above shows a thumbnail of the interactive Java applet embedded into this page. Unfortunately, your browser is not Java-aware or Java is disabled in the browser preferences. To start the applet, please enable Java and reload this page. (You might have to restart the browser.)

Circuit Description

This is the 1-bit adder block used in the carry-lookahead adder. It uses two XOR gates to calculate the si sum output bit of the ain, bin and cin (carry in) input bits.

Obviously, this block generates a carry output signal when both the ain and bin inputs are 1. Therefore, a simple AND gate is sufficient to compute the generate-carry signal on the gi output.

Similarly, the OR gate computes the propagate carry signal on the pi output.