Microprocessor 2

1Basic Definitions

In order to describe communication between components and electronic subunits, first we must cover general notions such as the direction of communication and connection topology, as well as the concepts of exchange synchronization and information coding, finishing off with the concept of a protocol, which defines the rules that have to be followed. A protocol also defines access arbitration and cycles.

1.1. General points regarding communication

The direction of communication between two systems (Figure 1.1) can either be one-way (simplex) or bidirectional, and this can be either a full-duplex or alternating (half-duplex). Note here that the communication protocol (i.e. the link layer) cannot provide more than what the physical layer permits.

Figure 1.1. Direction of transmission

The entity from which the communication originates and which is generating the address and control signals is called the Master (M) or Initiator (I), and is represented by a square in Figure 1.2. The entity that replies and follows the commands is traditionally called the Slave (S), or Target (T), and this is represented by a square in the figure. If the bus can only take a single master, it is referred to as a single master system. If it can take several it is called a multi-master system (cf. § 2.2.5). If the medium is shared during emission, there can be a conflict of access to ...