Abstract: A scan-cell for use in a scan device of the type which is utilized to test integrated circuits comprises a first multiplexer, a switching device, and a second multiplexer. The first multiplexer provides a data signal on the output thereof when a control signal is in a first state and provides a test signal at the output thereof when the control signal is in a second state. The switching device is coupled to the output of the first multiplexer and captures the output. The second multiplexer has an input coupled to the output of the switching device and transmits the output when the control signal is in the first state. The second multiplexer transmits an inverted form of the output when the control signal is in the second state.

Abstract: A base address prediction system for predicting one of a plurality of base addresses to be added to a known relative address in order to generate an absolute address. An actual base address determined from the relative address is also generated. The actual base address determination takes longer to generate than the predicted base address determination, and therefore the predicted base address is used to select a base address as long as the prediction is correct. Circuitry exists to compare the predicted base address with the actual base address, and if not equal, the predicted base address will be nullified, and the actual base address will be used. Prediction modes are dependent on whether the relative address indicates an instruction fetch or an operand fetch. Where the relative address indicates an instruction fetch, the prediction will be based on the last base address used, on the assumption that instructions will be contiguous in a single block of memory.

Abstract: An apparatus for and method of loading the addressing environment of a large scale multiprogrammed instruction processor. The addressing environment is normally loaded upon initiation of an application program. Providing a separate addressing environment for each application program permits the software to be developed using virtual addressing. The addressing environment is loaded to permit the instruction processor to convert the virtual addresses to absolute addresses. The addressing environment is specified by a stack of base registers. These are loaded sequentially from a data store containing the virtual address of the initial location of each data bank to be accessed. The virtual addresses are converted to absolute addresses for loading into the base registers. During the loading process, each virtual address is evaluated to determine if it defines a valid data bank. If it does, the corresponding base register is loaded.

Abstract: An apparatus for and method of loading the user addressing base register of a large scale multiprogrammed instruction processor. The base register is normally loaded to permit a user application program to access a different data segment. Providing a base register addressing environment for user application programs permits the software to be developed using virtual addressing. The addressing environment is specified by a stack of base registers. These are loaded from a data store specifying a virtual address for each data segment. During the loading process, an absolute address corresponding to the virtual address is loaded into each base register. To load a base register, a determination is made whether the future value differs from the previous value by a differential offset. If yes, the base register is loaded with an absolute address corresponding to the sum of the previous bank descriptor and the new offset. If no, the new base register value is computed by accessing a bank description table.