Control memory optimization for compositional microprogram control units with code sharing

The chapter considers some optimization methods used to reduce the size of CMCU control memory keeping the microprogram. These methods are based on the use of special address transformer permitting to keep the control memory size, which is the same as in case of the CMCU basic structure. One of the methods is oriented towards keeping only the original sets of microoperations and some additional variables in the control memory, in order to provide natural addressing and operation termination operating modes. The second approach assumes that a special CMCU block, which is not the part of its control memory, generates additional variables mentioned above. The methods proposed here permit to reduce control memory volume in comparison with the CMCU basic structure. Negative feature of this approach is decreasing of the CMCU performance because duration of the cycle becomes greater than in case of the CMCU basic structure.