Address formation in a microprogrammed data processing system

A data processing system comprising:

• A. an instruction register for storing an instruction word for indicating both a code of an operation to be performed in said system and an address indicator for pointing to a control word which is to provide control signals for effecting said operation indicated by said code;
• B. a control storage device having a plurality of said control words stored therein, each of said control words including a plurality of fields, said fields providing said control signals for controlling the operation of said system, one of said fields for indicating an address of the next location to be addressed dependent upon a specified test result;
• C. a memory device having a plurality of locations, each location for storing a word, some of said words including an operand;
• D. a base register for use primarily in storing a base address of a said location in said memory device;
• E. an index register for storing an index value for use with said base address in computing a final effective address of a said location in said memory device, said index value equal to zero if there is no such indexing required;
• F. a data register;
• G. means, responsive to the contents of said base register and said index register, for reading said operand from said memory device and writing said operand into said data register;
• H. means for transferring the contents of said data register into said instruction register so as to modify the code of operation;
• and
• I. control store device addressing logic, responsive to said address indicator in said instruction word in said instruction register and said field for indicating a next location address from a most recently addressed one of said control words, for generating said next location address of a location in said control storage device.