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Previous Year Exam Questions for Microprocessor and Interfacing - MPI of 2018 - vignan by Ashish Thakur

  • Microprocessor and Interfacing - MPI
  • 2018
  • PYQ
  • VFSTR U - vignan
  • Electronics and Communication Engineering
  • B.Tech
  • 24 Offline Downloads
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EC1303 – Microprocessor & Applications Question Bank  EC1303 – Microprocessor Microprocessor and Applications 2 Marks – Question & Answers Unit I (8085): 1. What are machine language and assembly language programs? The software developed using 1’s and 0’s are called machine language programs. The software developed using mnemonics are called assembly language programs. 2. Why data bus is bi-directional? The microprocessor has to fetch (read) the data from memory or input device for processing and after processing, it has to store (write) the data to memory or output device. Hence the data bus in microprocessor is bi-directional. 3. Why interfacing is needed for I/0 devices? Generally I/O devices are slow devices. Therefore the speed of I/O devices does not match with the speed of microprocessor. Therefore, an interface is provided between microprocessor and I/O devices. 4. What is data size in a microprocessor? The Data size is the size of the operand that can be processed by an ALU in a microprocessor. 5. Why EPROM is mapped at the beginning begin ning of memory space in 8085 system? In 8085 microprocessor, after a reset, the program counter will have the address 0000H. The monitor program is a permanent program for Initialization and configuring of peripherals and it is stored in the EPROM memory. If EPROM memory is mapped at the beginning of  memory space, i.e., at 0000H, then the monitor program will be executed automatically after a reset of the processor. This is why EPROM is mapped at the beginning of memory space. 6. What is Tri-state logic? A device can reside in three states, which are a) On-state b) Off-state and c) High impedance-state. The high impedance state is a state in which the output of a device is physically connected to a bus, but electrically isolated through high impedance. 7. Define Stack and Stack Pointer. Stack  is a portion of RAM memory which is used for temporary storage of register contents using PUSH and POP instructions. Stack Pointer (SP) is a 16-bit register that holds the memory address of the stack top. Stack pointer gets decremented by 2, for every push operation and vice versa. © NSS, 2008

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EC1303 – Microprocessor & Applications Question Bank  8. Define Program Counter. Program Counter  (PC) is a 16-bit register which holds the memory address of the instruction to be executed next. Program counter gets incremented by 1 for every execution of the instruction. 9. What is the significance of IO/M pin? IO/M pin is an I/O or Memory access indicator. It asserts to high level (1), when the processor access the I/O device and it goes to low level (0), when the processor access the memory for read/write operations. 10. State the function of HOLD and HLDA pins in 8085. The HOLD and HLDA pins in 8085 are used in interfacing the 8257-DMA controller IC with the processor. A signal is sent by 8257 to HOLD pin in µP, to request the µP to stop its current process and allocate the buses for DMA data transfer. µP acknowledges the request for DMA data transfer by 8257, by sending a signal in HLDA to 8257. 11. State the significance of X1 and X2 pins of 8085. The clock signal is supplied to the microprocessor 8085 by connecting either LC, RC or quartz crystal across the pins X 1 and X2. Out of the three, quartz crystal is preferred because of its high stability. 12. What is an Interrupt? How the interrupts are classified?  Interrupt  is a signal send by an external device to the processor (or special instruction executed in a program), to stop the execution of the current process in the microprocessor and perform a particular task (ie., data transfer) between the processor and the called device. They are three methods of classifying interrupts. Method I : The interrupts are classified into  Hardware and Software interrupts Method II : The interrupts are classified into Vectored  and Non-Vectored  interrupts. Method III : The interrupts are classified as  Maskable and Non-maskable interrupts. © NSS, 2008

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EC1303 – Microprocessor & Applications Question Bank  13. Distinguish I/O mapped I/O and memory mapped I/O. Mapping is the process by which the addresses are allocated to the I/O devices. The two kinds of mapping are a) Memory mapped I/O b) I/O mapped I/O Memory mapped I/O Standard I/O mapped I/O 1. 16-bit address is allotted to each I/O device. 1. 8-bit address is allotted to each I/O device. 2. The I/O devices are accessed by Memory Read or Memory Write machine cycles. 2. The I/O devices are accessed by I/O Read or I/O write machine cycles 3. All instructions related to memory can be used to access I/O devices. 3. Only IN and OUT instructions can be used to access I/O devices. 4. Large number of I/O devices can be interfaced. 4. Only small number of I/O devices can be interfaced. 5. Data transfer can be made between all registers and I/O devices. 5. Data transfer can be made only between Accumulator and I/O devices. 6. This scheme is used when complete memory space is required. 6. This scheme is used when memory requirement is less. 14. Explain the concept of demultiplexing AD0-7 lines in 8085? Demultiplexing is the process of separating the low byte Address (A 0-7) and Data (D0-7) from the multiplexed lines AD 0-7 lines of 8085, using a latch and Address latch enable (ALE) signal. When low byte address (A 0-7 ) comes out of AD0-7 lines, the processor asserts HIGH in the ALE pin, enabling the latch to separate the low byte address. © NSS, 2008

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EC1303 – Microprocessor & Applications Question Bank  15. What is memory mapping? The memory mapping is the process of interfacing memories to microprocessor and allocating addresses to each memory locations. 16. Explain the execution of the instruction CMA instruction in 8085. CMA instruction is used to perform 1’s complement of the contents of Accumulator in 8085. 17. What is the function performed by SIM and RIM instruction. SIM Instruction: The SIM instruction is used to mask the hardware interrupts RST7.5, RST6.5 and RST5.5. It is also used to send data through SOD line.  RIM Instruction: The RIM instruction is used to check whether an interrupt (RST7.5, RST6.5 and RST5.5) is masked or not. It is also used to read data from SID line. 18. What will be the outcome, in execution of instructions LXI H, 4600 H and LHLD 4600H? When LXI H,4600 is executed, the number 4600 will be loaded into HL register pair. When  LHLD 4600 is executed, the contents of memory location 4600 H and 4601H will be transferred into HL register pair. 19. Explain the function of IN and OUT instructions. Execution of an IN instruction will transfer one byte of data from an Input device to  Accumulator  of microprocessor. Execution of an OUT instruction will transfer one byte of data from Accumulator of  microprocessor to an Output device. 20. Compare System bus and CPU bus. Bus is a set of conducting wires in a microprocessor based system, which helps to carry various information like DATA, ADDRESS and CONTROL signals. Bus Internal CPU bus External System Bus System Bus It will not be directly connected to CPU There will be separate data, address & control buses CPU Bus It will be directly connected to CPU The data and address may be multiplexed  © NSS, 2008

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