4. (a) Design an asynchronous Binary Coded Decimal (BCD) count-up counter using JK flip-flops. Draw the counter circuit clearly showing the configuration of the JK flip-flops and the necessary logic gate(s). Sketch the input and output waveforms of this counter. (7 Marks) (b) The binary up/down counter for a cargo lift controller in a 7-storey building has an up-down (UID) control input and a buzzer output (B). The buzzer will sound (B = 1) when the lift is at level 1 or level 7. The configuration of the input is given in Table 2. Table 2 UID State 1 Count up 0 Count down For the binary up/down counter, (i) Draw the Moore model state diagram. (ii) Tabulate the excitation table based on D flip-flops. (iii) Plot the K-maps and write the characteristic equations. (iv) Realize the circuit using D flip-flops and NAND gates. 9 (15 Marks) (c) Discuss the one's catching problem in master-slave JK flip-flops, and explain why this problem does not occur in other edge-triggered flip-flops. END OF PAPER (3 Marks)