As seen in the previous half adder tutorial, it will produce two outputs, SUM and Carry out. ![]() The first half adder circuit is on the left side, we give two single bit binary inputs A and B. As I said, read the description and implement to solve that problem, don't just assume all enables work the same way. Let’s see the block diagram, Full adder circuit construction is shown in the above block diagram, where two half adder circuits added together with a OR gate. El is an input enable to determines if the register should be set from the input. Those previous enables, and EA and EB in this case, are output enables that feed to an OR for multiplexing. It is not implemented using a bunch of AND gates like many of the previous enables. The El logic for the register is completely different than the EA and EB logic. After completing the circuit, click Test to test it, then Submit to submit the quiz question result. ![]() Clock C high, then low should have no effect. Then set El low and set some other value on the ALU input pin. The register should be set to the value you entered when C goes back to 1. Set some four-bit input value on the ALU input pin. Turn on Show Output States so you can tell what is happening. To test your circuit manually, set Clow and El high. This leads to the very simple logic expression: CLK=C and ΕΙ. If EI is zero, a transition from 0 to 1 on C is ignored. You will latch the register when El is 1 and C transitions from 0 to 1. C and EI C is the clock input and EI is an enable. When EB is true, output B is the contents of the four-bit register. ![]() When EA is true, output A is the contents of the four-bit register. Notice: C is an input, NOT a clock! If you use a clock component you circuit will not pass tests! Outputs It will have two four-bit bus outputs named A and B. It will have two norma (single-bit) inputs: C and El. Your register will have these features: Inputs It will have one four-bit bus input named ALU that represents the arithmetic logic unit bus, the output of an ALU. In the Cirsim window below, implement a four-bit register.
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