Therefore, the sequence of operations to add the contents of register R₁ to register R₂ and store the result in register R3 should be as follows:

1. R_1out,      Y_in
2. R_2out,      Add,   Z_in
3. Z_out,        R3_in

In step 2 of this sequence, the contents of register R₂ are gated to the bus, hence to input –B of the ALU which is directly connected to the bus. The contents of register Y are always available at input A of ALU. The function performed by the ALU depends on the signal applied to the ALU control lines. In this example, the Add control line of ALU is set to 1, which indicate the addition operation and the output of ALU is the sum of the two numbers at input A and B. The sum is loaded into register Z, since the input gate is enabled (Z_in ). In step 3, the contents of register Z are transferred to the destination register R₃.

 

Question: Whether step 2 and step 3 can be carried out simultaneously.