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4.1 Name TWO methods to display information in digital systems - NSC Electrical Technology Digital - Question 4 - 2021 - Paper 1
Question 4
4.1 Name TWO methods to display information in digital systems. 4.2 Explain the term common anode with reference to the seven-segment LED display. 4.3 Refer to tra... show full transcript
Worked Solution & Example Answer:4.1 Name TWO methods to display information in digital systems - NSC Electrical Technology Digital - Question 4 - 2021 - Paper 1
Step 1
4.1 Name TWO methods to display information in digital systems.
Answer
Two methods to display information in digital systems include:
- Liquid Crystal Display (LCD): Utilizes liquid crystals to modulate light and display images or text.
- Light Emitting Diode (LED): Emits light when current flows through, commonly used in displays and indicators.
Step 2
4.2 Explain the term common anode with reference to the seven-segment LED display.
Answer
In a common anode seven-segment LED display:
- All the anodes (positive terminals) of the individual LED segments are connected together to a positive voltage source.
- Each segment is activated by grounding its respective cathode (negative terminal).
- This allows for a simple control mechanism to illuminate specific segments based on the binary input.
Step 3
4.3 Refer to transistor coupling as used in LED seven-segment displays and identify in the circuit FIGURE 4.3 below.
Answer
Transistor coupling in LED seven-segment displays involves using transistors to control the current flowing to the LED segments. When a transistor is turned on (saturated), it allows current to flow from the positive voltage source through the LED, thus illuminating it. The circuit in FIGURE 4.3 shows a transistor used for this purpose, with the base connected to a control signal.
Step 4
4.4 Explain the term polarisation of light with reference to liquid crystal display (LCD).
Answer
Polarisation of light refers to the orientation of light waves in a particular direction. In an LCD:
- Light travels through polarising filters which allow only light waves vibrating in a specific direction to pass.
- When the liquid crystals in the LCD are activated, they rotate the plane of polarisation of the light, allowing or blocking it from passing through the second polariser, which ultimately forms the images that we see on the display.
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4.6 On the ANSWER SHEET for QUESTION 4.6, draw the logic circuit of a full adder using AND gates, exclusive OR gates and an OR gate.
Answer
To construct a full adder:
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Use two XOR gates for the sum calculation:
- First XOR gate takes inputs A and B for sum S1.
- Second XOR gate takes S1 and Cin (carry input) for final sum S.
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Use two AND gates and one OR gate for carry output:
- First AND gate takes A and B for carry C1.
- Second AND gate takes S1 and Cin for carry C2.
- OR gate takes C1 and C2 to produce final carry output Cout.
Step 8
4.7 Complete the output waveforms on the ANSWER SHEET for QUESTION 4.7.
Answer
For the RS flip-flop in FIGURE 4.7:
- When S = 1 and R = 0, Q becomes 1, and Q' becomes 0.
- When S = 0 and R = 1, Q becomes 0, and Q' becomes 1.
- In the case S = 0 and R = 0, the states remain unchanged.
- These states are reflected as timing waveforms on the output graph.
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4.9 On the ANSWER SHEET for QUESTION 4.9, draw the circuit of a three-bit parallel adder.
Answer
The three-bit parallel adder can be designed by 3 full adders. Let the inputs be:
- A = A2 A1 A0
- B = B2 B1 B0
The outputs will be:
- S = S2 S1 S0 (sum)
- Cout (carry out)
Each full adder handles one bit and carries from the previous stage.
Step 11
4.10 Name TWO types of counters that are commonly used in digital electronics.
Answer
Two types of counters commonly used in digital electronics are:
- Asynchronous (Ripple) Counters: Where the flip-flops are driven by a single input clock, resulting in a ripple effect.
- Synchronous Counters: Where all flip-flops receive the clock signal simultaneously, providing more uniform timing.
Step 12
4.11 Explain the difference between combinational logic circuits and sequential logic circuits.
Answer
The primary differences are:
- Combinational Logic Circuits: These circuits output depend entirely on current inputs. They do not use memory storage and do not consider past inputs.
- Sequential Logic Circuits: These circuits utilize memory for past inputs, leading to outputs that depend on both current inputs and memory state.
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4.13 Name TWO types of shift registers, other than the serial-in; serial-out shift register.
Answer
Two other types of shift registers include:
- Parallel-in; Parallel-out Shift Register (PIPO): Data is loaded and retrieved in parallel format.
- Serial-in; Parallel-out Shift Register (SIPO): Data is entered serially but output in parallel.
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4.14.2 Explain the operation of this register.
Answer
The operation of a serial-in; serial-out shift register involves:
- Loading Data: Bits are transferred into the register one at a time, along with a clock pulse that enables the movement of data into each flip-flop sequentially.
- Data Shifting: After receiving the clock pulse, data shifts one position to the right for each subsequent pulse until the last flip-flop contains the last bit of data.
- Serial Output: The register outputs the bits in the same serial format, facilitating smooth data transfer.