Four 7-segment LED numeric displays for a 12-hour clock are shown below in Figure 2. The third LED display is inverted so that the decimal points of the second and third LED displays give the appearance of a
full colon. When the clock is switched on, it displays a random time and counts time by flashing the full
colon segments every second. When the RESET button is pressed the clock resets and displays 12:00 and
resumes counting time by flashing the full colon segments every second. It outputs hours with first and
second LED displays and outputs minutes with the third and fourth LED displays. The clock never displays
0.00.
1 Design the decoder for the third LED display. Draw the truth table for each segment of the display.
Write each segment of the display as a Boolean function. Implement the functions of the first two
segments as a 2-level logic circuits using NAND gates.
2 Design a 4-bit counter with synchronous LOAD and asynchronous CLEAR using SR flip-flops and
NAND gates. Draw the excitation table and derive the flip-flop input equations. Draw the logic
circuit of the 4-bit counter.
3 Using the MC14511-B and your design in question 1 code-named MD14511-X, design the 12-hour
clock with 4 LED displays as shown in Figure 2. Assume MD14511-X has the same number of pins
as the MC14511-B and the pins enable the same operations. Draw the detailed logic circuit of the 12-
hour clock showing the START switch and the RESET button. Print your design on an A3 sheet.
Ensure that the decimal points of the first and last LED displays are always disabled.