5.1 Explain polarisation when used in the operation of a liquid crystal display (LCD) - NSC Electrical Technology Digital - Question 5 - 2024 - Paper 1

In a common anode configuration, the anodes of all eight LEDs are connected to a common positive voltage rail, while the cathodes are connected to the individual segments. Conversely, in a common cathode configuration, all LED cathodes are tied together to a common 0 V, and the anodes are controlled independently.

To complete the block diagram of the three-bit parallel adder, you need to indicate two half adders along with their respective carry outputs. The first half adder will sum the least significant bits (A0 and B0), producing the output S0 and a carry-out C1. The second half adder will take the sum S0 from the first half adder and the next significant bits (A1 and B1) as inputs, yielding S1 and C2. Finally, an additional carry from the most significant bits (A2 and B2) will be added for the complete representation.

When switch 7 is pressed, the output will be determined by the binary configuration of the switches. Each switch represents a binary digit, and pressing switch 7 typically corresponds to the least significant bit being set. Identify which switches are closed and create the resulting binary code based on their positions.

Pulse triggering in flip-flops refers to the behavior of the circuit wherein it transitions states during the active (high) pulse period of the clock signal. This means that the flip-flop changes its output state at the rising or falling edge of the clock pulse, allowing it to synchronize with the clock signal accurately.

To complete the logic circuit for a full adder using two half adders, you need to connect the inputs A and B to the first half adder, producing sum S1 and carry C1. The second half adder accepts S1 and C in, producing the final sum output S and another carry C2. The outputs from the two half adders are combined with an OR gate to give the overall carry-out C out.

The logic circuit for a JK-type flip-flop consists of two AND gates and two inverters. Connect J and K inputs to the first AND gate along with the clock input. The output from this gate is then fed into the first inverter to set the Q output. The second AND gate takes the outputs from the first inverter alongside the clock to control the reset state.

To complete the waveforms for the JK flip-flop, begin with the clock and J, K inputs defined in the question. Since Q starts LOW, identify the transitions based on the J and K signals. Plot Q outputs reflecting the JK flip-flop's behavior in response to the defined clock pulse.

Output A, B, and C represent the count progression for the three-stage ripple counter. As Clock pulses arrive sequentially, you will need to track how each flip-flop toggles based on the input from the previous flip-flop.

The circuit in FIGURE 5.8 is asynchronous because each flip-flop toggles based on the output of the preceding flip-flop rather than all being driven by the same clock signal simultaneously.

One disadvantage of up/down counters is that they are generally slower than regular up or down counters due to the additional complexity of controlling both counting directions.

A four-bit serial-in: parallel-out shift register can be drawn using four D flip-flops connected in series. The serial input feeds into the first flip-flop, and the outputs are taken from each flip-flop for parallel output. Ensure to label the Clock and Clear lines for proper functionality.