Problem
Task I: Multiplexor
A modern home entertainment centre system may have a switch that selects music from one of four sources: an Ipod, a compact disc, a radio tuner, or a DVD player. The switch selects one of these four sources and sends the signal to the amplifier and speakers. This is basically what a multiplexer or MUX does: it selects one of several input signals and passes it through to the output. A digital multiplexer (also called data selector) is a logic circuit that selects one of several digital data inputs and passes it on to the output. The selection is controlled by the SELECT inputs (often referred to as the address inputs) which determine which data inputs will be switched to the output. Use Multisim to build a f4-input multiplexor using NAND gates only. How many SELECT inputs do you need? Use some switches and indicators to demonstrate that your multiplexor works correctly. Simulate and make screenshots.
Task II: Parallel register
Use four 74LS74 to make D-flip-flops to parallel in parallel out register which can store four bits. Demonstrate that it works by connecting a 4-bar LED to the outputs and switches to the inputs, including the clock inputs. Connect a CLR input to the Reset input so that you can reset all the flipflops at the same time. Preset should be connected to a switch or to VCC (if they are active low) if not used. Connect the outputs of all flip-flops to indicators to demonstrate that your circuit is working. Make screenshots.
Task III: Serial in registers
Use four 74LS74 D-flip-flops to make a serial in serial out register which can store 4 bits. How do the flip-flops need to be connected? Connect the relevant inputs, including the clock input to a swtich. Modify this register so that it becomes a serial in parallel out register. Demonstrate that both registers work. Preset and clear should be connected to separate switches or to VCC (if they are active low) if they are not used. Connect the outputs of all flip-flops to indicators to demonstrate that your circuit is working. Simulate and make screenshots.
Task IV: Parallel in serial out register
Use four 74LS74 D-flip-flops to make a parallel in serial out register which can store 4 bits. How do the flip-flops need to be connected? Please note that you now need an extra input to determine whether the data are loaded in or shifted. Label them clearly. Make sure you don't leave the preset and clear unconnected. Demonstrate that the register works and make screenshots.
Task V: Bidirectional register
Use four 74LS74 D-flip-flops to make a bidirectional register which can store four bits. How do the flip-flops need to be connected? Please note that you now need an extra input to determine wether the data are shifted left or right. Make sure you don't leave the preset and clear unconnected. Demonstrate that the register works and make screenshots.
Task VI: Johnson counter
In a Johnson counter the complement of the output of the last flip-flop is connected back to the D input of the first flip-flop. Use four 74LS74 D-flip-flops to make a 4-stage Johnson counter and demonstrate that it works and make screenshots.