4.1 Name TWO methods to connect the LEDs of an LED seven-segment display to the supply - NSC Electrical Technology Digital - Question 4 - 2020 - Paper 1

The circuit in FIGURE 4.2 represents a sourcing configuration for a digital output. It indicates a transistor switching circuit where the load (LED) is connected in series with the transistor.

1. Pulse Triggered Flip-Flops: These flip-flops respond to a short pulse in the timing signals.

2. Edge Triggered Flip-Flops: These flip-flops respond to the rising or falling edge of the clock signal.

Complete the diagram by ensuring the following connections: the inputs A and B should connect to the corresponding full adders, and the carry outputs should be routed from each full adder to the next.

The truth table should indicate the respective outputs for inputs A and B:

• For 00: Outputs 0 (1), 1 (0), 2 (0), 3 (0)
• For 01: Outputs 0 (0), 1 (1), 2 (0), 3 (0)
• For 10: Outputs 0 (0), 1 (0), 2 (1), 3 (0)
• For 11: Outputs 0 (0), 1 (0), 2 (0), 3 (1)

A decoder converts a binary code into a recognizable decimal form, either as a digit or a character.

1. Combinational Logic Circuits: These circuits output responses based solely on the current input values.
2. Sequential Logic Circuits: These circuits have memory elements and their outputs depend on current and past input values.

The truth table outlines the states of Q and Q' based on inputs S and R as follows:

• Illegal State: S = 1, R = 1 leads to both Q and Q' being undefined.
• Set State: S = 1, R = 0 sets Q to 1 and Q' to 0.
• Reset State: S = 0, R = 1 sets Q to 0 and Q' to 1.
• Hold State: S = 0, R = 0 maintains the current state.

The output waveforms should reflect the set and reset conditions based on the timing of the S and R inputs, capturing transitions that align with the truth table.

Propagation delay is the time taken for a signal to travel through a flip-flop or gate in a circuit. In asynchronous ripple counters, outputs of stages depend on the propagation delay of previous stages, leading to potential timing issues.

Propagation delay is when a change in input affects the output after a certain time. In asynchronous counters, this delay accumulates and can influence the counting accuracy across multiple stages.

The AND gate’s role is to control the output of the flip-flops based on specific conditions. It prevents incorrect readings of FF2 during clock transitions, thus ensuring proper sequential operation of the counter.

The register identified in FIGURE 4.12 is a 4-bit parallel-in-parallel-out shift register.

A = 4-bit data input B = 4-bit data output

The operation involves loading 4-bit data into the register on the clock pulse, transferring the data to the output pins, and allowing parallel access to the data stored within the register.