Abstract: Disclosed are methods and apparatus for multi-way program branching in a digital computer based on the contents of a data register. This is accomplished by loading any data field of interest into a data register and using the output lines as address lines to a plurality of read-only memory devices. Each device contains a set of random memory addresses. Logic circuits under program control select and enable one device, thereby producing one address. Finally, circuits under program control force a program branch to the location address produced. Thus, by programming the read-only memory devices and the computer appropriately, a plurality of sets of data fields are associated with and result in branches to a plurality of sets of locations, thereby giving the programmer the general capability of branching to any one of the plurality of locations within one instruction execution cycle based on the interrogation of any one data word.

Abstract: Circuits for the improved operation of microprogrammable computers are described. This improvement is accomplished by providing a set of read-only memory devices for storing the micro-code for all combinations of arithmetic logic unit function, carry bit and file register address than can be specified by an instruction word executed from Main Memory. In a universal microprogram designed to execute that family of Main Memory instructions that differ only in the functions specified above, the instruction word is used to address the read-only memory devices, the micro-code output of which is used to control the file, carry in bit and arithmetic logic unit. Through the use of these circuits a family of instructions may be executed by a single microprogram and at no increase in execution time over that required for the execution of a microprogram dedicated to a single instruction.

Abstract: A Read-Only Memory device in the CPU of a microprogrammable computer contains a diagnostic program suitable for self-testing the computer. A microprogram for loading this diagnostic program from the Read-Only Memory device into Main Memory is contained in the Control Memory of the CPU. When required, the diagnostic program is loaded into Main Memory and executed thus allowing for the testing of a computer without the need of operational peripherals.