The decoder of example 8.9 is to be used as a 1-of-16 demultiplexer. A logically compatible pulsed waveform is to be switched between output line 9 and line 15 when the logic status of an external control input is LOW and HIGH respectively. Draw the logic diagram indicating the logic status of

Question

The decoder of example 8.9 is to be used as a [latex]1-of-16[/latex] demultiplexer. A logically compatible pulsed waveform is to be switched between output line [latex]9[/latex] and line [latex]15[/latex] when the logic status of an external control input is LOW and HIGH respectively. Draw the logic diagram indicating the logic status of ENABLE inputs and DCBA inputs and the point of application of the pulsed waveform.

Accepted Answer

Figure 8.26 shows the logic diagram. When the external control input is in the logic LOW state, $D = HIGH$ , $C = LOW, B = LOW and A = HIGH$ . This means that output line $9$ is activated. When the external control input is in the logic HIGH state, $D = HIGH, C = HIGH, B = HIGH and A = HIGH$ . This means that output line $15$ is activated. In the logic diagram shown in Fig. 8.26, the two ENABLE inputs are tied together and the pulsed waveform is applied to a common point. This means that either both ENABLE inputs are active (when the input waveform is in the logic LOW state) or inactive (when the input waveform is in the logic HIGH state). Thus, when the input waveform is in the logic LOW state, output line 9 will be in the logic LOW state and all other output lines will be in the logic HIGH state provided the external control input is also in the logic LOW state. If the external

control input is in the logic HIGH state, logic LOW in the input waveform appears at output line $15$ . In essence, the logic status of the input waveform is reproduced at either line $9$ or line $15$ , depending
on whether the external control signal is LOW or HIGH.

control input is in the logic HIGH state, logic LOW in the input waveform appears at output line [latex]15[/latex]. In essence, the logic status of the input waveform is reproduced at either line [latex]9[/latex] or line [latex]15[/latex], depending
on whether the external control signal is LOW or HIGH.

Question 8.10: The decoder of example 8.9 is to be used as a 1-of-16 demult...

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