______ devices are used to tell a circuit what to do and when to do it.

In the context of digital electronics, processing devices are integral components that interpret input signals and execute specific actions based on programmed instructions. These devices include microcontrollers, microprocessors, and digital signal processors, which are designed to handle data computations and control logic in a circuit. They operate by receiving input signals—whether from sensors or other sources—then processing these inputs to produce an appropriate output signal, thereby dictating what action the circuit should take and the timing of that action.

While sensing devices detect conditions or changes in the environment, actuation devices carry out physical actions based on instructions, and transmitting devices are involved in the communication between components, it is the processing devices that effectively make decisions and instruct the entire system on operational functions. Thus, the role of processing devices is pivotal in determining the behavior of a circuit within digital electronics.