Binary decoder circuit

Using the characteristics of the circuit shown in Fig. 7.1, we can add AND gates and create a binary decoder circuit. The binary decoder circuit looks at two input signals and determines whether the signal corresponds to a 0, 1, 2, or 3. The truth table for the binary decoder is shown in Table 7.1. 

Figure 7.7 Breadboard results of the binary decoder circuit (0 and 1).

Figure 7.6 shows the schematic of the complete circuit schematic that provides this logic function. The binary counter circuit (Fig. 7.1) provides the input signals, and the AND gates provide the decoder logic. The clock signal is 100 KHz at 50% duty cycle. 

By using 16-bit encoder/decoder ICs, the direct transmission of 16-bit data is possible (Figure 30.7) and this eliminates the binary adder circuit required for converting 8-bit data to 16-bit data. A 16-bit data-transmission scheme uses 16-bit encoder/decoder ICs (e.g., GL116 [Glolab Corporation, United States]). The transmitter module transmits the 16-bit serial data for the receiver to be converted to 16-bit parallel data. 

The state diagram of the decoder circuit is shown in Figure 7.2. There are five states. The coding scheme associated with each transition shows the inputs required to make the transition and the outputs drat transition produces. The inputs to die decoder are latched and so it stays in each state until the input changes but will only issue a pulse to the encoder when it first enters the state. The next correct ntunber makes the transition to the next number state whereas an incorrect number will reset the system. The CLEARbuttonondiekeypadisencoded with the binary value III and in this case can simply be treated as an incorrect input. 

Scanning circuits are typically made out of a binary counter and a decoder (for example, an LS93 and an LS138) whose output lines successively activate the open collector or trl-state circuits that connect the various decades to the bus, and select the appropriate digit. Some LSI circuits, like the six decade 7301, already Include the scanning circuits. 

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