Signal logic-level

Some TTL parts have three-state outputs totem pole outputs that have the added feature that both output transistors can be turned off under the control of an output enable signal. When the output enable is in its active state, the part s output functions conventionally, but when the enable is inactive, both transistors are off, effectively disconnecting the output pin from the internal circuitry. Several three-state outputs can be connected to a common bus, and only one output is enabled at a time to selectively place its logic level on the bus. 

What are the input and output requirements of the system Specify all signal current and voltage ranges, logic levels, input and output impedances, digital codes, data rates, and data formats. 

Race elimination. Race conditions can exist in the circuit because there was no accounting for the period of time for which a signal stays at a particular logic level between events. Three types of race conditions are possible not enough time to synchronize an event before another on the same wire cancels it out a set or reset AND condition that may never be true because one of the input events is followed too closely by another on the same wire and a set or reset condition that is true at other times during the sequence of events and will cause an unwanted setting or resetting to occur. 

Figure 11.3 shows a simulation trace of the DAIO phase decoder using the Mercury logic-level simulator [MKMT90]. The phase decoder monitors the biphased coded data stream data from the audio device and extracts the following synchronization signals preamble-1, preamble-2, and preamble-3. 

It is very important that such molecular-level motions are accompanied by changes of some chemical or physical property of the system, resulting in a readout signal that can be used to monitor the operation of the machine. The reversibility of the movement ie, the possibility to restore the initial situation by means of an opposite stimulus, is an essential feature of a molecular machine. Since such induced motions correspond to a binary logic systems of this kind could also prove useful for information processing. 

Figure 2. (a) Electronic representation, (b) truth table, and (c) molecular implementation of YES (PASS) logic. 0 and 1 are digital representations of low and high signal levels respectively in all Figures. 

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