Control unit

New features:

Fig. 5.17

Instruction bit numbers for register numbers, opcode, function

MUX to select destination register

RegDst: selects $rd or $rt to write data

ALU control: uses function code and ALUOp to generate ALU operation selection

What is ALUOp?  2-bit code generated by main control (stay tuned)

Note that the values of RegDst, ALUSrc, and PCSrc are reversed in this diagram.

The version in the current printing of the text is correct.