Immediate Operand

OR Operation on Bits first operand 0 0 1 1 second operand 0 1 0 1   __ __ __ __ result 0 1 1 1

A machine instruction can use some of its bits as one of the operands for a machine operation. This is called an immediate operand. For example, here is one of the instructions from the previous example program:

address         machine code      assembly code
——————————      ——————————        ————————————
0x00400000      0x34080002        ori $8,$0,0x2
                      ----

The last 16 bits (four nibbles) of the machine instruction contain the operand 0x0002. (The assembly language instruction can just say "0x2"). The machine instruction tells the ALU to perform a bitwise OR between the contents of register $0 and the immediate operand 0x0002. The result is put in register $8.

A bitwise operation is where a logical operation is performed on the bits of each column of the operands. Here is the bitwise OR between two 8-bit patterns:

0110 1100    operand
0101 0110    operand
---------
0111 1110    result