Diagnostics in Computer Controlled Equipment

Publisher Summary This chapter discusses diagnostics in computer controlled equipment. The store for the instructions, usually held in non-volatile read only memory, ROM. The store for other data generated during the execution of the program and usually comprising random access memory, RAM. The CPU communicates with the instruction and data stores and with the interfaces to the equipment under control via a multi-way bus that, in many systems, carries time division multiplexed addresses, data, and program instructions. Closed loop diagnostics are those where the computer both applies the test stimulus and monitors its result. Most control computers spend a substantial amount of time effectively idle, waiting for an external event to occur to which they must respond. Open loop diagnostics are those that involve both the computer and an operator. Either the computer generates and applies a stimulus signal but an operator observes and interprets its effects or the operator applies a stimulus signal to which the computer responds. The stimulus sequence must be designed to cause at least one change of state at all nodes to be tested or several sequences will be required. It is necessary to specify the points in the circuit from which the start and stop signals for the sampling period are to be obtained and the clock phase to be used.