Microprocessor & Microcontroller Question With Answer 8085
1. What is Microprocessor? Give the power supply & clock frequency of 8085 ?
Ans:- A microprocessor is a multipurpose, programmable logic device that reads binary instructions from a storage device called memory accepts binary data as input and processes data according to those instructions and provides results as output. The power supply of 8085 is +5V and the clock frequency is 3MHz.
2. List few applications of microprocessor-based systems.
Ans:- It is used:
- i. For measurements, display and control of current, voltage, temperature, pressure, etc.
- ii. For traffic control and industrial tool control.
- iii. For speed control of machines.
3. What are the functions of an accumulator?
Ans:- The accumulator is the register associated with the ALU operations and sometimes I/O operations. It is an integral part of ALU. It holds one of the data to be processed by ALU. It also temporarily stores the result of the operation performed by the ALU.
4. List the 16 – bit registers of the 8085 microprocessor.
Ans:- Stack pointer (SP) and Program counter (PC).
5. List the allowed register pairs of 8085.
Ans:-
- B-C register pair
- D-E register pair
- H-L register pair
6. Mention the purpose of SID and SOD lines.
Ans:-
- SID (Serial input data line): It is an input line through which the microprocessor accepts serial data.
- SOD (Serial output data line): It is an output line through which the microprocessor sends output serial data.
7. What is an Opcode?
Ans:- The part of the instruction that specifies the operation to be performed is called the operation code or opcode.
8. What is the function of the IO/M signal in the 8085?
Ans:- It is a status signal. It is used to differentiate between memory locations and I/O operations. When this signal is low (IO/M = 0) it denotes the memory-related operations. When this signal is high (IO/M = 1) it denotes an I/O operation.
9. What is an Operand?
Ans:- The data on which the operation is to be performed is called an Operand.
10. Control signals used for DMA operation are ?
Ans:- HOLD & HLDA.
11. What is meant by interrupt?
Ans:- Interrupt is an external signal that causes a microprocessor to jump to a specific subroutine.
12. Explain priority interrupts of 8085.
Ans:- The 8085 microprocessor has five interrupt inputs. They are TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. These interrupts have a fixed priority of interrupt service. If two or more interrupts go high at the same time, the 8085 will service them on priority basis. The TRAP has the highest priority followed bye RST 7.5, RST 6.5, RST 5.5. The priority of interrupts in 8085 is shown in the table.
| Interrupts | Priority |
|---|---|
| TRAP | 1 |
| RST 7.5 | 2 |
| RST 6.5 | 3 |
| RST 5.5 | 4 |
| INTR | 5 |
13. What is a microcomputer?
Ans:- A computer that is designed using a microprocessor as its CPU is called a microcomputer.
14. What is the signal classification of 8085.
Ans:- All the signals of 8085 can be classified into 6 groups.
- Address bus
- Data bus
- Control and status signals
- Power supply and frequency signals
- Externally initiated signals
- Serial I/O ports
15. What are operations performed on data in 8085.
Ans:- The various operations performed are
- Store 8-bit data
- Perform arithmetic and logical operations
- Test for conditions
- Sequence the execution of instructions
- Store data temporarily during execution in the defined R/W
- memory locations called the stack
16. Steps involved to fetch a byte in 8085.
Ans:-
- i. The PC places the 16-bit memory address on the address bus.
- ii. The control unit sends the control signal RD to enable the memory chip.
- iii. The byte from the memory location is placed on the data bus.
- iv. The byte is placed in the instruction decoder of the microprocessor and the task is carried out according to the instruction.
17. How many interrupts does 8085 have, mention them.
Ans:- The 8085 has 5 interrupt signals; they are INTR, RST7.5, RST6.5, RST5.5 and TRAP.
18. What is an instruction?
Ans:- An instruction is a binary pattern entered through an input device to command the microprocessor to perform that specific function.
19. What is the use of ALE.
Ans:- The ALE is used to latch the lower order address so that it can be available in T2 and T3 and used for identifying the memory address. During T1 the ALE goes high, the latch is transparent ie, the output changes according to the input data, so the output of the latch is the lower order address. When ALE goes low the lower order address is latched until the next ALE.
20. Explain the signals HOLD, READY and SID.
Ans:- HOLD indicates that a peripheral such as DMA controller is requesting the use of address bus, data bus and control bus. READY is used to delay the microprocessor read or write cycles until a slow responding peripheral is ready to send or accept data. SID is used to accept serial data bit by bit.
21. Explain the different instruction formats with examples.
Ans:- The instruction set is grouped into the following formats.
- One byte instruction:- MOV C, A
- Two byte instruction:- MVI A,39H
- Three byte instruction:- JMP 2345H
Part- 2
1. On which model is based the basic architecture of a digital computer?
Ans:- The basic architecture of a digital computer is based on Von Neumann model.
2. What is meant by distributed processing?
Ans:- Distributed processing involves the use of several microprocessors in a single computer system. For example, for such a system, the first microprocessor may control keyboard activities, the second controls storage devices like disk drives, the third controls input/ output operations, while the fourth may act as the main system processor.
3. What is the technology used in microprocessor?
Ans:- NMOS technology is used in microprocessors.
4. How does the microprocessor communicate with the memory and input/output devices?
Ans:- The microprocessor communicates with the memory and input/output devices via three buses, viz., data bus, address bus and control bus.
5. What are the different jobs that the CPU is expected to do at any given point of time?
Ans:- The CPU may perform a memory read or write operation, an I/O read or write operation or an internal activity.
6. What is mnemonic?
Ans:- It is very difficult to understand a program if it is written in either binary or hex code. Thus the manufactures have devised a symbolic code for each instruction, called a mnemonic.
7. What is machine language programming?
Ans:- Programming a computer by utilizing hex or binary code is known as machine language programming.
8. How many different instructions microprocessor 8085 has? What is an instruction set?
Ans:- 8085 microprocessor has a total 74 different instructions for performing different operations or tasks. The entire different instructions that a particular microprocessor can handle is called its instruction set.
9. What an instruction consists of?
Ans:- An instruction consists of an operation code (called opcode) and the address of the data (called operand), on which the opcode operates.
10. In how many groups can the signals of 8085 be classified?
Ans:- The signals of 8085 can be classified into seven groups according to their functions. These are:
- (a) Power supply and frequency signals
- (b) Data and Address buses
- (c) Control bus
- (d) Interrupt signals
- (e) Serial I/O signals
- (f) DMA signals
- (g) Reset signals
11. What is the operating frequency of 8085?
Ans:- 8085 operates at a frequency of 3 MHZ, and the maximum frequency of operation is 500 KHz. The versions 8085 A-2 operates at a maximum frequency of 5 MHz.
12. What is the purpose of CLK signal of 8085?
Ans:- The CLK (out) signal obtained from pin 37 of 8085 is used for synchronizing external devices.
13. What are the temporary registers of 8085?
Ans:- The temporary registers of 8085 are temporary data register W and Z registers. These registers are not available to the programmer, but 8085 uses them internally to hold temporary data during execution of some instructions.
14. In what other way HL pair can be used?
Ans:- HL register pair can be used as a data pointer or memory pointer.
15. Describe the Status Register of 8085?
Ans:- Explain the Flag registers and the structure.
16. What is the purpose of increment/decrement address latch register?
Ans:- These 16-bit registers increment/decrement the contents PC or SP when instructions related to them are executed.
17. What is an instruction?
Ans:- An instruction is a command which asks the microprocessor to perform a specific task or job.
18. What is meant by instruction set?
Ans:- The entire different instructions that a particular microprocessor can handle is called its instruction set.
19. What are the different types of data transfer operations possible?
Ans:- The different types of data transfer operations possible are cited below;
- Between two registers.
- Between a register and a memory location.
- A data byte can be transferred between a register and a memory location.
- Between an I/O device and the accumulator.
- Between a register pair and the stack.
The term ‘data transfer’ is a misnomer – actually data is not transferred, but copied from source to destination.
20. Explain the two instructions (a) LDAX and (b) STAX.
Ans:- The instruction LDAX indicates that the contents of the designated register pair point to a memory location and copies the content of the memory location into the accumulator.
As an example: let D=40H, E= 50H and memory location 4050H =AB H. Then LDAX D transfers the contents of memory location 4050H to the accumulator. Thus, after the execution of instruction, ACC = AB H.
Before execution location instruction
STAX stands for ‘store accumulator indirect’. The contents of the accumulator are copied into the memory location specified by the contents of the register pair. As an example, let D=40 H and E = 50 H and ACC = AB H. Then STAX D stores the accumulator contents in the memory location 4050 H.
21. What happens when HLT is executed in software?
Ans:- All the buses go into tri-state on execution of HLT instruction.
22. Explain DAA instruction with example?
Ans:- It stands for ‘decimal adjust accumulator’. Execution of DAA instruction converts the contents of the accumulator into two BCD values. The system utilities the AC flag (not accessible by the programmer, but is used internally for DAA operation) for this conversion by following the procedure stated below,
- (a) If the lower order 4-bits (D3 – D0) of the accumulator is greater than 910 or if the AC flag is set, then this instruction (i.e., DAA) adds 0610 to the low-order 4-bits.
- (b) If the higher order 4-bits (D7 - D4) of the accumulator is greater than 910 or if the CY flag is set, then this instruction (i.e., DAA) adds 6010 to the high –order 4 – bits.
EXAMPLE: Discussed in the class
23. What the instruction DCR M stands for?
Ans:- Here the memory location M is pointed to by the content of HL register pair. On executing DCR M, the content of the memory location is decremented by 01. Thus, if the memory location, as pointed to by HL register pair is AB H, then DCR M makes the content of that memory location to be AA H.
25. What is stack?
Ans:- A stack is a group of memory locations in the R/ W.
26. How the stack is intialised?
Ans:- The stack is initialised by a 16 – bit register, called the stack pointer (SP) register.
27. What type of memory is the stack?
Ans:- Stack is a ‘last-in first-out’ or LIFO type memory. This means that data which is pushed last into stack is popped out of it first.
28. How the stack is initialised?
Ans:- The stack is initialised by means of the stack pointer. The software instruction is like this: LXI SP, 0033H. It means that the stack is initiated at the memory location 3300 by the stack pointer.
29. By how many memory locations SP is decremented/incremented when PUSH/ POP instruction is performed?
Ans:- SP is decremented/ incremented by the two memory locations when PUSH/POP is executed.
30. What is a subroutine?
Ans:- A subroutine is a group of instructions, written separately from the main program, which performs a function that is required repeatedly in the main program.
31. Why a subroutine is used in a program?
Ans:- Since a subroutine is called more than once by the main program, thus, use of subroutines saves subroutine, hexa-decimal converter subroutine, display subroutine is called by the main program, the more is the saving of memory space.
32. Explain nesting of subroutines.
Ans:- The process of a subroutine calling a second subroutine and the second subroutine in its turn calling a third one and so on is called nesting of subroutine. Theoretically speaking, the number of subroutines that can be called by this process is infinite but, in practice it is limited by the size of memory.
33. Write a program which will store the contents of accumulator and flag register at 2000H and 2001H memory locations respectively. (Using PUSH & POP instructions)
Ans:- The following is the program for the above, using PUSH – POP instructions.
- LXI SP, 4000 H: Accumulator
- PUSH PSW: Accumulator and flag register contents pushed into stack
- POP B: Accumulator content goes to B and flag register content goes C register
- MOV A, B: Content of B taken to accumulator
- STA 2000H: Accumulator content stored into memory location 2000 H
- MOV A, C: Content of C moved to accumulator
- STA 2001H: Accumulator content stored into memory location 2001 H
- HLT: Program halted
34. What is the function of S0 & S1.
Ans:-
35. Explain the difference between JMP and CALL instructions?
Ans:- WIKIPEDIA
36. Why do you use XRA A instruction?
Ans:- The XRA A instruction is used to clear the contents of the Accumulator and store the value 00H.
37. Compare CALL and PUSH instructions?
Ans:-
38. Compare RET and POP instructions?
Ans:-
39. Write the Evolution of Microprocessors?
Ans:- SEARCH WIKIPEDIA
40. What is memory capacity? How it can be expressed?
Ans:- Memory capacity is specified with the product of address (i.e. 2n. Where ‘n’ is the number of address bit) and data line.
- (a) Generally memory capacity can be expressed as, Memory capacity = Address * Data.
- (b) The standard expressions are, 1 KB, 2 KB, 16 KB etc.
41. How memory address lines are calculated for a given memory location?
Ans:- The following procedure are used for calculation of memory address line i.e. log (2x) = log (memory locations)
- => x log (2) = log (memory locations)
- => x = log (memory location) / log (2)
42. What is memory capacity? How it can be expressed?
Ans:- Memory capacity is specified with the product of address (i.e. 2n. Where ‘n’ is the number of address bit) and data line.
- (a) Generally memory capacity can be expressed as, Memory capacity = Address * Data.
- (b) The standard expressions are, 1 KB, 2 KB, 16 KB etc.
43. Write the comparison between static RAM & Dynamic RAM.
Ans:- SEARCH WIKIPEDIA
44. Explain in brief the difference Read-Only Memory.
Ans:- The different kinds of Read-only Memory is given below,
(a) PROM (b) EPROM (c) EEPROM (d) MASKED ROM (e) FLASH MEMORY
45. (Write an assembly language program) Ten number 8-bit data are stored starting from memory location 2100H. Transfer this entire block of data to a memory location starting from 3100H.
Ans:-
MVI B, 0A H
LXI H, 2100 H
LXI D, 3100 H
LOOP: MOV A, M
STAX D
INX H
INX D
DCR B
JNZ LOOPHLT
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