The following figure shows the datapath with main control and ALU control and the control signals.
The input to the main control unit is the 6-bit opcode field from the instruction. The outputs of the main control unit consist of 10 1-bit control signals:
- three signals that are used to control multiplexors (
RegDst,ALUSrc, andMemtoReg), - three signals for controlling reads and writes in the register file and data memory (
RegWrite,MemRead, andMemWrite), - three signals sent to the “Next PC” logic for determining whether to possibly jump, branch-on-equal, or branch-on-not-equal, and
- a signal for sign-extending 16-bit immediate to 32 bits.