ISCET Digital Systems & Microprocessors 2 — Questions and Answers
Question 1: In a microprocessor system, what is the function of the program counter (PC)?
- Stores the result of the last arithmetic operation
- Holds the memory address of the next instruction to be fetched (Correct answer)
- Counts the number of instructions executed
- Stores temporary data during arithmetic operations
Correct answer: Holds the memory address of the next instruction to be fetched
The program counter holds the address of the next instruction to be fetched from memory, automatically incrementing after each fetch.
Question 2: Which addressing mode uses the instruction itself to contain the data value rather than an address?
- Direct addressing
- Indirect addressing
- Immediate addressing (Correct answer)
- Indexed addressing
Correct answer: Immediate addressing
Immediate addressing embeds the actual data value directly within the instruction, eliminating the need for a separate memory access.
Question 3: What logic function does a half adder implement?
- Adds two bits and produces a sum and carry-out (Correct answer)
- Adds three bits and produces a sum and carry-out
- Subtracts two binary numbers
- Multiplies two single-bit values
Correct answer: Adds two bits and produces a sum and carry-out
A half adder takes two single-bit inputs and outputs a sum (XOR) and carry-out (AND), but cannot handle a carry-in.
Question 4: In a microprocessor, what is a 'bus cycle'?
- The clock period of the CPU
- The time to complete one read or write transaction on the system bus (Correct answer)
- The number of bits transferred per second
- The frequency of the system oscillator
Correct answer: The time to complete one read or write transaction on the system bus
A bus cycle is the sequence of events required to complete a single data transfer (read or write) between the CPU and memory or I/O.
Question 5: Which flip-flop type changes output state only on the active clock edge when both J and K inputs are HIGH?
- SR flip-flop
- D flip-flop
- T flip-flop
- JK flip-flop (Correct answer)
Correct answer: JK flip-flop
The JK flip-flop toggles its output when both J=1 and K=1 on the active clock edge, resolving the forbidden state of the SR flip-flop.
Question 6: What is the decimal equivalent of the two's complement binary number 11110110?
- -10 (Correct answer)
- -16
- -6
- -12
Correct answer: -10
Inverting 11110110 gives 00001001, adding 1 gives 00001010 = 10, so the value is -10.
Question 7: In a PLA (Programmable Logic Array), what is programmed by the user?
- Only the AND plane
- Only the OR plane
- Both the AND plane and the OR plane (Correct answer)
- Neither plane — the architecture is fixed
Correct answer: Both the AND plane and the OR plane
A PLA allows programming of both the AND array (product terms) and the OR array (sum of products), offering maximum flexibility.
ISCET Digital Systems & Microprocessors 2
In a microprocessor system, what is the function of the program counter (PC)?