Figure 12.1 A simpliﬁ ed block diagram of a digital television set-top box
The use of such a hierarchical approach aids understanding of systems and makes fault ﬁ nding and repair of complex systems possible without the need to interpret design details within every block of the system. The complexity of integrated circuits (ICs) that are used in modern systems, and the increasing complexity of systems themselves mean that most electronic devices and equipment cannot usefully be treated as an arrangement of simple circuit components. Breaking the functions of a system down into functional system modules, with deﬁ ned inputs and outputs, typically makes description and understanding easier and quicker. Although a module is an item that has clearly deﬁ ned inputs and outputs, at block diagram level, it may cut across physical boundaries of printed circuit boards or complex chips in an actual device. A module could be a small part of a single IC, or an entire printed circuit board. The advantage of considering any electronic device as a set of modules in this way is that you do not require a detailed knowledge of how a module works in order to test its input and output signals and determine
whether it is faulty. Normally, in consumer electronic devices a faulty module requires the replacement of the whole circuit board on which it is located, and any form of servicing work at the component level is now rare (and may be too expensive in labour costs).