An assembler approach to the automation of test vector generation

Two schemes for testing user logic in a microcontroller-based ASIC are described. The direct access method consists of multiplexing primary signals with the microcontroller´s signals at the interface with user logic. Multiplexing allows the designer to mimic the microcontroller core´s application of stimuli to user logic using a predefined test mode. During test mode, the designer has both the controllability and the observability to directly test the user logic. This method bypasses whatever method is used for testing the microcontroller core and peripherals. Alternatively, the core access method utilizes the microcontroller core to test user logic. To reduce the customer´s burden, the standard microcontroller assembler has been enhanced to aid in test vector generation. The extended assembler allows customers to generate stimuli and monitor responses which are synchronized with the bus cycles of the microcontroller core. This method of testing user logic is complementary to and dependent on the method of testing the microcontroller core and peripherals. Advantages and disadvantages of each approach are described. Three examples are explored to compare and contrast these two testing methods