Each instruction has its own OPCODE (Operation Code),
which is analog to the assembly mnemonic in machine
language. The length in bits of the OPCODE depends on the
bits required to represent the total number of instructions. As
the complete set contains 20 instructions, 5 bits are enough
to represent them.
As said, operands are the most important factor, the
reason is that this factor makes necessary to reclassify the
instructions like follows [8]:
• Type J (Jumps)
• Type I (Immediate data)
• Type R (Registered operations)
Type J instructions only use the OPCODE and an 8 bit
constant value (k); Type I Instructions use the OPCODE, a
destiny (Rd) or source (Rs) register and a constant value (k);
while Type R instructions require a single destination
register or both: destination and source register.