Q. Characteristics of extreme unencoded micro-instructions?

1. Two sources can be attached by respective control signals to a single destination; though only one of these sources can be used at aninstance. So combinations where both these control signals are active for same destination are redundant.

2. A register can't act as a destination and a source at the same instance. So such a combination of control signals is redundant.

3. We can offerjust one pattern of control signals at aninstance to ALU making some of combinations redundant.

4. We can offerjust one pattern of control signals at aninstance to external control bus also.

So we don't require 2N combinations. Presume we only require 2K (that is less than 2N) combinations then we require only K encoded bits in place of N control signals. K bit micro-instruction is an extreme encoded micro-instruction.