Question

Although the control unit as a whole requires 50 ps, it so happens that we can extract the correct value of the reg2loc control wire directly from the instruction. thus, the value of this control wire is available at the same time as the instruction. explain how we can extract this value directly from the instruction

Answer 1

Answer:

The value of Reg2loc refers to a control signal given to the mux to select the value and given as input to read the Register 2.

Explanation:

Solution

The value of Reg2loc refers to a control signal given to the mux to select the value and given as input to read the Register 2.

• The mux selects 0-4 bits from the Rt field, when the value Reg2loc is 1

• The mux selects 20-16 bits from the Rm field, when is 0.
• From the figure 2.20 shown, the 11 bits (21.31) of the opcode field from the instruction. but, it is not useful to in knowing the value of Regloc control value

• Since, the Reg2loc signals value choose either 0-4 bits or 20-16 bits this is not determined by the opcode.

Note: Although the control unit as a whole requires 50 ps, it so happens that we can extract the correct value of the reg2loc control wire directly from the instruction. thus, the value of this control wire is available at the same time as the instruction. explain how we can extract this value directly from the instruction

Hints: Carefully examine the opcodes shown in Figure 2.20. Also, Remember that LSR and LSL do not use the Rm field. Finally, ignore STXR.)