Some instructions, such as branches, jumps, and stores, do not write to a register. For the instructions that do write to a register, the destination register can be one of the following.

• The register specified by the rd field (R-type instructions)
• The register specified by the rt field (I-type instructions)
• $ra (jal instruction)

The MIPS single-cycle implementation diagram does not include signal handling for $ra.

The value to be written to the register can come from the following places.

• The ALU (arithmetic and logical instructions)
• Memory (load instructions)
• The incremented PC (jal and jalr instructions)

The MIPS single-cycle implementation diagram does not include signal handling for the incremented PC.