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5.1 Explain the term common cathode with reference to the seven-segment LED display - NSC Electrical Technology Digital - Question 5 - 2021 - Paper 1
Question 5
5.1 Explain the term common cathode with reference to the seven-segment LED display. 5.2 Draw a fully labelled circuit diagram of a sinking digital output. Indicate... show full transcript
Worked Solution & Example Answer:5.1 Explain the term common cathode with reference to the seven-segment LED display - NSC Electrical Technology Digital - Question 5 - 2021 - Paper 1
Step 1
Explain the term common cathode with reference to the seven-segment LED display.
Answer
A common cathode seven-segment display consists of multiple individual light-emitting diodes (LEDs) that illuminate segments to form numbers or characters. In this configuration, all the cathodes of the segments are internally connected to ground. When a positive voltage is applied to the anodes of specific segments, the corresponding LED lights up. This setup allows for easier control of the display, as the common ground returns the current.
Step 2
Draw a fully labelled circuit diagram of a sinking digital output. Indicate the direction of current flow at the output.
Answer
To depict a sinking digital output, draw a circuit that includes a power source (+V), a transistor (e.g. NPN), a resistor, and a load (e.g. an LED). The collector of the transistor connects to the load, while the emitter is grounded. The base of the transistor is connected to a control signal. When the control signal is HIGH, the transistor conducts, allowing current to flow through the load to ground, indicating a sinking configuration. Current direction is from the load to ground when the circuit is completed.
Step 3
Explain the function of the encoder in FIGURE 5.3.
Answer
The encoder in FIGURE 5.3 converts decimal input data from switches (S1, S2, S3) into binary format. It detects the position of the active switch and translates that into a binary output represented at A0 and A1. For example, if S1 is pressed, the output will reflect the binary equivalent of the corresponding decimal number, effectively encoding the information for further processing.
Step 4
Step 5
Draw the labelled logic circuit for the logic symbol in FIGURE 5.4 using AND gates and NOR gates only on the ANSWER SHEET for QUESTION 5.4.
Answer
In this logic circuit, the SET and RESET inputs are connected to AND gates with the clock signal feeding into both gates. The outputs from these gates are then fed into a NOR gate to produce Q and its complement Q'. The configuration ensures that the flip-flop retains its state unless triggered by the clock signal, illustrating how the flip-flop stores and alters data based on the inputs.
Step 6
Draw the logic circuit of a half-adder using an AND gate and an Exclusive-OR gate.
Answer
The half-adder consists of an AND gate and an Exclusive-OR (XOR) gate. The inputs A and B are connected to both gates. The output of the XOR gate represents the sum (Σ), while the output of the AND gate signifies the carry-out (Cₒ). This arrangement allows the half-adder to perform addition on two binary digits.
Step 7
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Step 9
Explain the difference between the full-sequence counter and the truncated counter.
Answer
A full-sequence counter counts through all possible states until it reaches its maximum count, whereas a truncated counter is designed to stop counting before reaching its maximum. This makes truncated counters useful in applications requiring limited counting ranges, such as modulo-n counting.
Step 10
Explain the term positive edge triggering.
Answer
Positive edge triggering refers to the operation of a digital circuit responding to the rising edge of a clock signal. This means that changes to the state of the circuit occur when the clock transitions from low to high. It ensures precise timing for data capture and state changes.
Step 11
Refer to FIGURE 5.9 below and explain the sequential operation of this counter without the aid of a truth table.
Answer
In FIGURE 5.9, the counter begins from a low state. FF0 and FF2 control the higher bits while FF1 acts as the middle bit. The clock input drives the transition of these flip-flops. When the counter receives clock pulses, it increments its output until it reaches the desired decimal number (10 in binary form) and subsequently holds that state, preventing further increments until reset or disabled.
Step 12
Draw a neatly labelled diagram of a four-bit serial-in: parallel-out shift register using D-type flip-flops. Show ALL the inputs and outputs.
Answer
For the shift register, draw four D-type flip-flops arranged in a series. Each D flip-flop has inputs for Data In (serial), Clock, and Clear. The outputs Q1, Q2, Q3, and Q4 represent parallel outputs. Data is shifted through each flip-flop on the rising edge of the clock, allowing it to store four bits of data in a parallel format.