Explain bit-O-Ring technique.
The micro program represents that branches are not always made to a one branch address. This is a direct consequence of combining easy micro routines by sharing common parts. Consider a point in the micro program sequencing. At this point, it is essential to choose between actions needed by direct and indirect addressing modes. If the indirect mode is specified in the instruction, then the microinstruction in the location 170 is performed to get the operand from the memory. If the direct mode is specified, this get must be bypassed by branching immediately to location 171. The most efficient way to bypass microinstruction 170 is to have the preceding branch microinstructions state the address 170 and then use an OR gate change the least significant bit of this address to '1' if the direct addressing mode is included. This is known as the bit-O-ring technique for modifying branch address.