Representation of Signals

Representation of Signals

Before going to see the timing diagram, we will see the signals and its representation used in the timing diagrams.

Clock Signal : The 8085 divides the clock frequency provided at x 1 and x2 inputs by 2, which is called operating frequency. All the operations within the 8085 are synchronized with this operating frequency. Therefore in the timing diagram operating frequency clock is shown on the top and then the signals are shown with reference to operating frequency clock. Ideally, the clock signal should be square wave with zero rise time and fall time, as shown in the Fig. 5.2.1. But in practice, we do not get zero rise time and fall time. Therefore the clock and other signals are always shown with finite rise and fall times. Fig. 5.2.1 shows the practical way of representing clock signal.

Single Signal : Single signal is represented by a line. It may have status either logic 0 or logic 1 or tri-state. The change in the state of the signal takes finite time and hence the state change of signal is represented with finite rise time and fall time, as shown in the Fig. 5.2.2.

Group of Signals :

Group of signals is also called a bus e.g. address bus and data bus. To avoid complications in the timing diagram these signals are grouped and shown in the form of block as shown in Fig. 5.2.3.

In the group representation individual state is not considered, but the group state is considered. Change in state of single signal changes the state of group. It is represented by the cross as shown the Fig. 5.2.3. The tri-state condition of the group signals is shown by dotted lines. Two straight lines represent valid state/stable state.

In microprocessor systems, activation of signal/signals depends on the state of other signal/signals. Such situations are shown in the timing diagrams with the help of specific symbols. There are four possibilities :

Activation of a signal with the change in state of other signal.

Activation of a signal with the change in state of other signals.

Activation of signals with the change in state of other signal.

Activation of signals with the change in state of other signals.

Fig. 5.2.4 shows the representation of dependence of the signal/signals, in the timing diagram.

 Review Questions

1. What is clock signal ?

2. Show the representation of single signal.

3. Show the representation of group of signals.