Microprocessor architecture having internal access means

Abstract

A single-chip processor architecture is disclosed which permits the registers and control latches of the processor to be easily accessed without using instructions to achieve such access. The architecture provides for an internal access (IA) function which is enabled by applying an IA Request signal to an IA terminal of the processor. During the IA function, program execution in the processor is suspended and the registers and control latches may be accessed as if they were storage locations in a random access memory. After the IA function is enabled, the address of a register or control latch selected for access is applied to the Address/Data port of the processor, and an IA Control Code specifying the strobing of the Address/Data port is applied to the Status terminals of the processor. After strobing of the address, a second IA Control Code specifying either reading or writing of the selected register or control latch is applied to the Status terminals. If the second Control Code specifies reading, the contents of the selected register or control latch is provided at the Address/Data port. If the second Control Code specifies writing, data received at the Address/Data port is stored in the selected register. The IA function facilitates program development in the processor because it provides an efficient means for observing the internal machine states and register contents of the processor. Functional testing of the processor is also facilitated because the IA function increases the availability of the internal nodes of the processor chip for the application of test signals and for the observation of circuit responses.