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RRB MCQs

Practice RRB-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 701
Microprocessors & MicrocontrollersFundamentals

A microcontroller typically integrates which elements on a single chip?

  • ACPU, memory and peripheral interfaces
  • BOnly an ALU
  • COnly RAM
  • DOnly a clock generator
Report an error
Correct Answer: A. CPU, memory and peripheral interfaces
Explanation: A microcontroller commonly combines CPU, program/data memory and peripherals such as I/O ports and timers on one chip.
Reference: Standard microprocessors and microcontrollers: fundamentals
Question 702
Microprocessors & MicrocontrollersCPU Architecture

The ALU in a processor is mainly responsible for?

  • AArithmetic and logical operations
  • BLong-term program storage only
  • CGenerating AC power
  • DMechanical input switching
Report an error
Correct Answer: A. Arithmetic and logical operations
Explanation: The arithmetic logic unit performs operations such as addition, subtraction, AND, OR and comparisons.
Reference: Standard microprocessors and microcontrollers: cpu architecture
Question 703
Microprocessors & MicrocontrollersCPU Architecture

The program counter normally contains?

  • AAddress of the next instruction to be fetched
  • BCurrent arithmetic result
  • CStack data only
  • DPower-supply voltage
Report an error
Correct Answer: A. Address of the next instruction to be fetched
Explanation: The program counter tracks the address from which the next instruction is to be fetched.
Reference: Standard microprocessors and microcontrollers: cpu architecture
Question 704
Microprocessors & Microcontrollers8085 Instructions

The instruction MOV B,C in the 8085 performs what operation?

  • ACopies contents of C into B
  • BCopies B into C
  • CAdds B and C
  • DClears both B and C
Report an error
Correct Answer: A. Copies contents of C into B
Explanation: The 8085 MOV destination,source format copies the source operand into the destination, so B receives C.
Reference: Standard microprocessors and microcontrollers: 8085 instructions
Question 706
Microprocessors & MicrocontrollersCPU Architecture

The accumulator in many classic microprocessors is mainly used to?

  • AHold operands and arithmetic/logic results
  • BStore the entire operating system
  • CGenerate address-bus timing only
  • DReplace ROM permanently
Report an error
Correct Answer: A. Hold operands and arithmetic/logic results
Explanation: The accumulator is a central register used by many arithmetic and logic instructions.
Reference: Standard microprocessors and microcontrollers: cpu architecture
Question 708
Microprocessors & MicrocontrollersBus Organization

The address bus is normally used to carry?

  • AAddresses of memory or I/O locations
  • BOnly arithmetic results
  • CClock pulses only
  • DPower to peripherals
Report an error
Correct Answer: A. Addresses of memory or I/O locations
Explanation: The address bus identifies the memory or I/O location involved in a transfer.
Reference: Standard microprocessors and microcontrollers: bus organization
Question 709
Microprocessors & Microcontrollers8085 Instructions

The 8085 JMP instruction is used for?

  • AUnconditional transfer of program control to a specified address
  • BAddition of two registers
  • CLoading immediate data into the accumulator
  • DReturning from a subroutine
Report an error
Correct Answer: A. Unconditional transfer of program control to a specified address
Explanation: JMP address loads the program counter with the specified target address without testing a condition.
Reference: Standard microprocessors and microcontrollers: 8085 instructions
Question 710
Microprocessors & MicrocontrollersBus Organization

The data bus carries?

  • AData between processor, memory and peripherals
  • BOnly addresses
  • COnly reset signals
  • DOnly interrupt priorities
Report an error
Correct Answer: A. Data between processor, memory and peripherals
Explanation: The data bus transfers instruction bytes and data among system components.
Reference: Standard microprocessors and microcontrollers: bus organization
Question 711
Microprocessors & Microcontrollers8085 Instructions

The 8085 CALL instruction is primarily used to?

  • AInvoke a subroutine while saving the return address
  • BClear all registers
  • CDisable the clock
  • DPerform multiplication directly
Report an error
Correct Answer: A. Invoke a subroutine while saving the return address
Explanation: CALL transfers control to a subroutine and saves the return address on the stack so execution can later resume after a RET.
Reference: Standard microprocessors and microcontrollers: 8085 instructions
Question 714
Microprocessors & Microcontrollers8085 Basics

The 8085 is fundamentally an?

  • A8-bit microprocessor
  • B16-bit microcontroller
  • C32-bit DSP only
  • D4-bit memory chip
Report an error
Correct Answer: A. 8-bit microprocessor
Explanation: The Intel 8085 is classified as an 8-bit microprocessor because its main data operations and data bus are 8 bits wide.
Reference: Standard microprocessors and microcontrollers: 8085 basics
Question 715
Microprocessors & Microcontrollers8085 Basics

The 8085 has an address bus of?

  • A8 bits
  • B12 bits
  • C16 bits
  • D20 bits
Report an error
Correct Answer: C. 16 bits
Explanation: The 8085 provides 16 address lines, allowing 2^16 addressable byte locations.
Reference: Standard microprocessors and microcontrollers: 8085 basics
Question 717
Microprocessors & Microcontrollers8085 Basics

The 8085 data bus width is?

  • A4 bits
  • B8 bits
  • C16 bits
  • D20 bits
Report an error
Correct Answer: B. 8 bits
Explanation: The 8085 has an 8-bit bidirectional data bus.
Reference: Standard microprocessors and microcontrollers: 8085 basics
Question 719
Microprocessors & Microcontrollers8085 Registers

In the 8085, the accumulator is an?

  • A8-bit register
  • B16-bit register
  • C20-bit register
  • D1-bit register
Report an error
Correct Answer: A. 8-bit register
Explanation: The 8085 accumulator A is an 8-bit register used extensively by arithmetic and logic instructions.
Reference: Standard microprocessors and microcontrollers: 8085 registers
Question 720
Microprocessors & Microcontrollers8085 Flags

Which of the following is an 8085 flag?

  • AZero flag
  • BDMA flag
  • CUSB flag
  • DEthernet flag
Report an error
Correct Answer: A. Zero flag
Explanation: The 8085 flag register includes Sign, Zero, Auxiliary Carry, Parity and Carry flags.
Reference: Standard microprocessors and microcontrollers: 8085 flags
Question 722
Microprocessors & Microcontrollers8085 Flags

The Carry flag in the 8085 is particularly used to indicate?

  • ACarry out or borrow condition associated with arithmetic
  • BInstruction address only
  • CClock failure
  • DMemory refresh only
Report an error
Correct Answer: A. Carry out or borrow condition associated with arithmetic
Explanation: The Carry flag records carry/borrow information from arithmetic operations and is also affected by certain rotate operations.
Reference: Standard microprocessors and microcontrollers: 8085 flags
Question 724
Microprocessors & Microcontrollers8085 Stack & Subroutines

Which 8085 instruction is used to return from a subroutine?

  • ACALL
  • BJMP
  • CRET
  • DRST
Report an error
Correct Answer: C. RET
Explanation: RET pops the saved return address from the stack into the program counter.
Reference: Standard microprocessors and microcontrollers: 8085 stack & subroutines
Question 725
Microprocessors & Microcontrollers8085 Stack & Subroutines

During a normal 8085 CALL instruction, the return address is stored on the?

  • AStack
  • BAccumulator
  • CFlag register only
  • DData bus permanently
Report an error
Correct Answer: A. Stack
Explanation: CALL pushes the return address onto the stack before transferring control to the subroutine.
Reference: Standard microprocessors and microcontrollers: 8085 stack & subroutines
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Question 726
Microprocessors & Microcontrollers8085 Stack & Subroutines

In the 8085, the stack normally grows toward?

  • AHigher memory addresses
  • BLower memory addresses
  • COnly I/O addresses
  • DThe reset vector
Report an error
Correct Answer: B. Lower memory addresses
Explanation: PUSH/CALL operations decrement the stack pointer, so the 8085 stack grows toward lower memory addresses.
Reference: Standard microprocessors and microcontrollers: 8085 stack & subroutines
Question 728
Microprocessors & Microcontrollers8085 Addressing Modes

Which 8085 addressing mode is used in the instruction MVI A,32H?

  • AImmediate addressing
  • BRegister addressing
  • CDirect addressing
  • DRegister indirect addressing
Report an error
Correct Answer: A. Immediate addressing
Explanation: The operand 32H is included directly in the instruction, so MVI A,32H uses immediate addressing.
Reference: Standard microprocessors and microcontrollers: 8085 addressing modes
Question 729
Microprocessors & Microcontrollers8085 Interrupts

Which 8085 interrupt has the highest hardware priority?

  • AINTR
  • BRST 5.5
  • CRST 6.5
  • DTRAP
Report an error
Correct Answer: D. TRAP
Explanation: TRAP is the highest-priority hardware interrupt in the 8085.
Reference: Standard microprocessors and microcontrollers: 8085 interrupts
Question 730
Microprocessors & Microcontrollers8085 Addressing Modes

Which addressing mode is used by the 8085 instruction MOV A,B?

  • AImmediate
  • BRegister
  • CDirect
  • DRegister indirect
Report an error
Correct Answer: B. Register
Explanation: Both source and destination operands are CPU registers, so MOV A,B uses register addressing.
Reference: Standard microprocessors and microcontrollers: 8085 addressing modes
Question 731
Microprocessors & Microcontrollers8085 Interrupts

Which 8085 hardware interrupt is non-maskable?

  • ATRAP
  • BRST 7.5
  • CRST 6.5
  • DINTR
Report an error
Correct Answer: A. TRAP
Explanation: TRAP cannot be disabled by the normal interrupt masking mechanism and is therefore non-maskable.
Reference: Standard microprocessors and microcontrollers: 8085 interrupts
Question 732
Microprocessors & Microcontrollers8085 Addressing Modes

Which addressing mode is used by the 8085 instruction LDA 2050H?

  • ARegister
  • BImmediate
  • CDirect
  • DImplied
Report an error
Correct Answer: C. Direct
Explanation: LDA contains the 16-bit memory address of the operand explicitly, so it uses direct addressing.
Reference: Standard microprocessors and microcontrollers: 8085 addressing modes
Question 735
Microprocessors & Microcontrollers8085 Interrupts

Which 8085 interrupt is non-vectored and requires external hardware to supply an instruction during interrupt acknowledge?

  • ATRAP
  • BRST 7.5
  • CRST 5.5
  • DINTR
Report an error
Correct Answer: D. INTR
Explanation: INTR is a general-purpose non-vectored interrupt; the external device must provide an instruction, commonly an RST opcode, during interrupt acknowledge.
Reference: Standard microprocessors and microcontrollers: 8085 interrupts
Question 737
Microprocessors & Microcontrollers8085 Interrupts

The 8085 instruction EI is used to?

  • AEnable maskable interrupts
  • BDisable all clock signals
  • CEnable only TRAP
  • DErase interrupt vectors
Report an error
Correct Answer: A. Enable maskable interrupts
Explanation: EI enables the maskable interrupt system after its specified activation behavior; TRAP is non-maskable.
Reference: Standard microprocessors and microcontrollers: 8085 interrupts
Question 739
Microprocessors & Microcontrollers8085 Instructions

The 8085 instruction INX H performs which operation?

  • AIncrements HL pair by one
  • BIncrements only H by one
  • CAdds HL to accumulator
  • DLoads HL from memory
Report an error
Correct Answer: A. Increments HL pair by one
Explanation: INX operates on a 16-bit register pair, so INX H increments HL by one.
Reference: Standard microprocessors and microcontrollers: 8085 instructions
Question 742
Microprocessors & Microcontrollers8085 Logical Instructions

If A=3CH in the 8085, executing CMA produces?

  • AC3H
  • B3DH
  • CCCH
  • D00H
Report an error
Correct Answer: A. C3H
Explanation: CMA complements every accumulator bit. The one's complement of 3CH (00111100) is C3H (11000011).
Reference: Standard microprocessors and microcontrollers: 8085 logical instructions
Question 744
Microprocessors & Microcontrollers8085 Interrupts

The 8085 instruction DI is used to?

  • ADisable maskable interrupts
  • BDisable TRAP permanently
  • CDecrease the accumulator
  • DDisable the address bus
Report an error
Correct Answer: A. Disable maskable interrupts
Explanation: DI disables maskable interrupts; it does not disable the non-maskable TRAP input.
Reference: Standard microprocessors and microcontrollers: 8085 interrupts
Question 745
Microprocessors & Microcontrollers8085 Timing

A T-state in a microprocessor corresponds to?

  • AOne period of the processor clock
  • BOne complete program
  • COne memory chip
  • DOne interrupt vector only
Report an error
Correct Answer: A. One period of the processor clock
Explanation: A T-state is one clock period and is the basic timing unit used to describe machine cycles.
Reference: Standard microprocessors and microcontrollers: 8085 timing
Question 748
Microprocessors & Microcontrollers8085 Timing

If the 8085 READY input is low, the processor can insert?

  • AWait states
  • BExtra interrupts only
  • CReset cycles only
  • DDMA addresses only
Report an error
Correct Answer: A. Wait states
Explanation: READY allows slower memory or I/O devices to extend a bus cycle by causing the processor to insert wait states.
Reference: Standard microprocessors and microcontrollers: 8085 timing
Question 749
Microprocessors & Microcontrollers8085 Interfacing

The 8085 HOLD and HLDA signals are primarily associated with?

  • ADirect memory access
  • BSerial arithmetic
  • CSoftware interrupts
  • DBCD adjustment
Report an error
Correct Answer: A. Direct memory access
Explanation: An external DMA controller can assert HOLD; the processor responds with HLDA after relinquishing the buses.
Reference: Standard microprocessors and microcontrollers: 8085 interfacing
Question 750
Microprocessors & Microcontrollers8085 I/O Interfacing

Memory-mapped I/O in an 8085 system uses?

  • AThe memory address space and memory-type instructions
  • BOnly an 8-bit isolated port address
  • CNo address lines
  • DOnly RST instructions
Report an error
Correct Answer: A. The memory address space and memory-type instructions
Explanation: Memory-mapped I/O assigns peripheral registers addresses in the memory space, allowing memory-reference instructions to access them.
Reference: Standard microprocessors and microcontrollers: 8085 i/o interfacing
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Question 751
Microprocessors & Microcontrollers8086 Architecture

The Intel 8086 is fundamentally a?

  • A16-bit microprocessor
  • B8-bit microcontroller
  • C4-bit processor
  • D32-bit DSP
Report an error
Correct Answer: A. 16-bit microprocessor
Explanation: The 8086 has a 16-bit ALU and 16-bit external data bus and is classified as a 16-bit microprocessor.
Reference: Standard microprocessors and microcontrollers: 8086 architecture
Question 755
Microprocessors & Microcontrollers8086 Architecture

The 8086 Bus Interface Unit is responsible for functions including?

  • AInstruction fetching and physical address generation
  • BOnly arithmetic multiplication
  • COnly flag comparisons
  • DOnly interrupt masking
Report an error
Correct Answer: A. Instruction fetching and physical address generation
Explanation: The BIU handles bus operations, instruction fetching, segment registers and physical-address generation.
Reference: Standard microprocessors and microcontrollers: 8086 architecture
Question 756
Microprocessors & Microcontrollers8086 Architecture

The 8086 instruction prefetch queue has a capacity of?

  • A2 bytes
  • B4 bytes
  • C6 bytes
  • D8 bytes
Report an error
Correct Answer: C. 6 bytes
Explanation: The 8086 BIU can prefetch up to six instruction bytes into its queue.
Reference: Standard microprocessors and microcontrollers: 8086 architecture
Question 760
Microprocessors & Microcontrollers8086 Segmentation

The 8086 physical address is calculated from segment and offset as?

  • ASegment × 16 + offset
  • BSegment + offset only
  • CSegment × 256 + offset
  • DOffset × 16 + segment
Report an error
Correct Answer: A. Segment × 16 + offset
Explanation: A segment value is shifted left by four bits, equivalent to multiplying by 16, and the offset is then added.
Reference: Standard microprocessors and microcontrollers: 8086 segmentation
Question 761
Microprocessors & Microcontrollers8085 Interfacing

In the 8085, the lower-order address bus AD0-AD7 is multiplexed with the?

  • AData bus
  • BInterrupt bus
  • CClock bus
  • DPower bus
Report an error
Correct Answer: A. Data bus
Explanation: AD0-AD7 carry the low-order address during the first part of a machine cycle and data during later parts.
Reference: Standard microprocessors and microcontrollers: 8085 interfacing
Question 766
Microprocessors & Microcontrollers8086 Addressing Modes

The 8086 instruction MOV AX,[BX] uses which addressing concept for the memory operand?

  • ARegister indirect addressing
  • BImmediate addressing
  • CImplied addressing
  • DPort addressing only
Report an error
Correct Answer: A. Register indirect addressing
Explanation: BX contains the effective offset address of the memory operand, making this a register-indirect memory reference.
Reference: Standard microprocessors and microcontrollers: 8086 addressing modes
Question 767
Microprocessors & Microcontrollers8086 Addressing Modes

In 8086 immediate addressing, the operand is?

  • AIncluded in the instruction itself
  • BAlways stored at address 00000H
  • CAlways in the stack
  • DSupplied only by an interrupt
Report an error
Correct Answer: A. Included in the instruction itself
Explanation: An immediate operand is encoded as part of the instruction.
Reference: Standard microprocessors and microcontrollers: 8086 addressing modes
Question 770
Microprocessors & Microcontrollers8086 Segmentation

For 8086 address 1234H:0010H, the physical address is?

  • A12340H
  • B12350H
  • C12440H
  • D01244H
Report an error
Correct Answer: B. 12350H
Explanation: 1234H×10H=12340H; adding 0010H gives 12350H.
Reference: Standard microprocessors and microcontrollers: 8086 segmentation
Question 771
Microprocessors & Microcontrollers8086 Segmentation

For 8086 address 2000H:1234H, the physical address is?

  • A21234H
  • B32340H
  • C201234H
  • D03234H
Report an error
Correct Answer: A. 21234H
Explanation: 2000H×10H=20000H; adding 1234H gives 21234H.
Reference: Standard microprocessors and microcontrollers: 8086 segmentation
Question 772
Microprocessors & Microcontrollers8086 Segmentation

The maximum size of one logical 8086 segment is?

  • A16 KB
  • B32 KB
  • C64 KB
  • D1 MB
Report an error
Correct Answer: C. 64 KB
Explanation: The 16-bit offset can range from 0000H to FFFFH, so a segment can span up to 64 KiB.
Reference: Standard microprocessors and microcontrollers: 8086 segmentation
Question 773
Microprocessors & Microcontrollers8051 Serial Communication

The 8051 serial port is commonly described as?

  • AFull-duplex
  • BHalf-duplex only
  • CSimplex transmit-only
  • DParallel-only
Report an error
Correct Answer: A. Full-duplex
Explanation: The 8051 serial interface can transmit and receive simultaneously, so it supports full-duplex communication.
Reference: Standard microprocessors and microcontrollers: 8051 serial communication
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Question 776
Microprocessors & Microcontrollers8051 Serial Communication

In the classic 8051, the serial transmit-complete flag is?

  • ATI
  • BRI
  • CTF0
  • DIE0
Report an error
Correct Answer: A. TI
Explanation: TI is set when a serial transmission completes according to the selected serial mode.
Reference: Standard microprocessors and microcontrollers: 8051 serial communication
Question 777
Microprocessors & Microcontrollers8051 Serial Communication

In the classic 8051, the serial receive flag is?

  • ATF1
  • BRI
  • CTR0
  • DIT0
Report an error
Correct Answer: B. RI
Explanation: RI indicates that a serial data frame has been received and is ready for software handling.
Reference: Standard microprocessors and microcontrollers: 8051 serial communication
Question 778
Microprocessors & Microcontrollers8051 Interrupts

The classic 8051 provides how many standard interrupt sources?

  • A3
  • B5
  • C8
  • D16
Report an error
Correct Answer: B. 5
Explanation: The standard 8051 has five interrupt sources: external 0, Timer 0, external 1, Timer 1 and serial port.
Reference: Standard microprocessors and microcontrollers: 8051 interrupts
Question 780
Microprocessors & Microcontrollers8051 Architecture

The classic Intel 8051 is fundamentally an?

  • A8-bit microcontroller
  • B16-bit microprocessor
  • C32-bit DSP
  • D4-bit memory controller
Report an error
Correct Answer: A. 8-bit microcontroller
Explanation: The original 8051 is an 8-bit microcontroller with an 8-bit CPU and integrated memory/peripheral resources.
Reference: Standard microprocessors and microcontrollers: 8051 architecture
Question 785
Microprocessors & Microcontrollers8051 Registers

The 8051 DPTR register is how many bits wide?

  • A8 bits
  • B16 bits
  • C20 bits
  • D32 bits
Report an error
Correct Answer: B. 16 bits
Explanation: DPTR is a 16-bit data pointer composed of DPH and DPL.
Reference: Standard microprocessors and microcontrollers: 8051 registers
Question 787
Microprocessors & Microcontrollers8051 Interfacing

During external memory access in the 8051, Port 0 is multiplexed to carry?

  • ALow-order address and data
  • BOnly high-order address
  • COnly interrupt signals
  • DOnly serial data
Report an error
Correct Answer: A. Low-order address and data
Explanation: Port 0 serves as multiplexed AD0-AD7 for the low address byte and data bus during external-memory cycles.
Reference: Standard microprocessors and microcontrollers: 8051 interfacing
Question 788
Microprocessors & Microcontrollers8051 Interfacing

During external memory access, 8051 Port 2 commonly carries?

  • AHigh-order address byte
  • BOnly low-order data
  • CTimer overflow
  • DSerial receive data only
Report an error
Correct Answer: A. High-order address byte
Explanation: Port 2 supplies A8-A15 when the 8051 accesses external memory.
Reference: Standard microprocessors and microcontrollers: 8051 interfacing
Question 791
Microprocessors & Microcontrollers8051 Timers & Interrupts

In the 8051, the TCON register contains control/status bits associated with?

  • ATimers and external interrupts
  • BSerial baud data only
  • CProgram memory only
  • DPort 0 pull-ups only
Report an error
Correct Answer: A. Timers and external interrupts
Explanation: TCON includes timer run/overflow bits and external-interrupt control/flag bits.
Reference: Standard microprocessors and microcontrollers: 8051 timers & interrupts
Question 798
Measurements & InstrumentationMeasurement Fundamentals

Measurement is the process of comparing an unknown quantity with?

  • AAn accepted standard
  • BA random signal
  • COnly a digital display
  • DA power supply
Report an error
Correct Answer: A. An accepted standard
Explanation: Measurement determines the magnitude of a quantity by comparison with an accepted reference or standard.
Reference: Standard measurements and instrumentation: measurement fundamentals
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