Digital Electronics with Arduino: Learn How to Work with Digital Electronics and Microcontrollers by Bob Dukish

Author:Bob Dukish [Dukish, Bob]
Language: eng
Format: epub
Publisher: BPB Publications
Published: 2020-08-15T00:00:00+00:00

Figure 5.2: A 4-bit shift register

The main difference in this circuit that is readily apparent is that the Q outputs connect to the D inputs of the flip-flops. As the clock cycles occur, the data coming from the data in line moves in a step-by-step manner through each of the flip-flops. After four clock cycles, the register in our example is fully loaded and can be shifted out in parallel, or after 4 more clock cycles, the 4 bits of data can be shifted out serially through the pin shown as out in Figure 5.2. As with the memory storage register of Figure 5.1, bus interfacing circuits using the tristate buffer would be used to reduce loading effects. To construct a parallel-in serial-out register, additional switching circuitry would need to be added between each Q output and D input so as to disconnect the Q outputs when loading since it would require that logic levels would need to connect to the D pins and Q outputs must never have a logic level applied to them or damage would result.

Shift registers are a part of a communications system incorporated in a digital device called a Universal Asynchronous Receiver Transmitter (UART). The UART is used when connecting through USB, and also found in modems. Figure 5.3 shows the part of the Arduino Uno, where USB communication takes place:

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