Arrangement for micro instruction control

In a modularly structured data processing system controlled by microinstructions, said system including plural data processing modules, a central source of microprogrammed control signals common to said modules, first bus means having plural bit lines for transferring control bit signals in parallel form from said central source to said modules, a central source of data signals common to said modules, second bus means having plural bit lines for transferring data bit signals in parallel form from said central source of data signals to said modules, the improvement for selectively transferring additional control bit signals to said modules through selected bit lines in said second bus means which intermittently are not used for transferring data bits, wherein said central source of control bit signals includes a first control store for storing microinstruction words having operation code syllables, first decoding means coupled to said first control store for producing said control bit signals in response to microinstruction word outputs of said first control store, means coupling outputs of said first decoding means to said first bus means for transferral to said modules, comprising:

• a decoder internal to each said module for decoding control bit signals to generate control signals for internal control of data bit processing operations in the respective module;
• and
• coupling means internal to each said module for coupling control bit signals to the respective decoder from all of the bit lines in said first bus means, and for coupling additional control bit signals to the respective decoder from said selected lines in said second bus means;
• each said decoder being responsive to control bit signals coupled thereto by said respective coupling means for operating selectively in first and second modes;
• each said decoder being operative in said first mode to decode said control bit signals and additional control bit signals in combination and in said second mode to decode only said control bit signals for generating control signals for controlling the internal data bit processing operations in the respective module.