If we connect the transistors as shown in the figures, we will create the memory of one bit. The moment we bring the voltage, it is uncertain which of the transistors will be the first to go into saturation and conduct. If the right transistor starts conducting first, the voltage on its collector is 0V which completely cuts off the left transistor and output Q is 0. If the left transistor starts conducting first, the voltage on the collector of the right transistor is 5V and the output Q is 1. However, if we introduce control signals S (set ) and R (reset), we will be able to control the circuit. By applying high voltage to the S input, the left transistor will conduct and the right will be cut-off and the circuit will result in Q output 1. Conversely, by applying high voltage to the R input, the right transistor will conduct and the left will be cut-off and the circuit will result in Q output 0. What makes the circuit particularly interesting is the fact that the circuit will remember the state even after the cessation of control signals. The table below formally describes these conditions, and it is important to emphasize that the high voltage to both control inputs at the same time is prohibited. In this case, the transistors will race in order to conduct and the state is uncertain.
It is convenient to note that our circuit does not differ much from the circuit with which we created the transistor oscillator. All this speaks in favor of the ubiquity and applicability of transistors, the basic building blocks.
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