Short Question And Answer Microprocessor Set-8

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1. What is the information that can be obtained from the status word of 8251?
The status word can be read by the CPU to check the readiness of the transmitter or receiver and to check the character synchronization in synchronous reception. It also provides information regarding various errors in the data received. The various error conditions that can be checked from the status word are parity error, overrun error and framing error.

2. What are the tasks involved in keyboard interface?
The task involved in keyboard interfacing are sensing a key actuation, Debouncing the key and Generating key codes (Decoding the key).These task are performed software if the keyboard is interfaced through ports and they are performed by hardware if the keyboard is interfaced through 8279.

3. How a keyboard matrix is formed in keyboard interface using 8279?
The return lines, RLo to RL7 of 8279 are used to form the columns of keyboard matrix. In decoded scan the scan lines SLo to SL3 of 8279 are used to form the rows of keyboard matrix. In encoded scan mode, the output lines of external decoder are used as rows of keyboard matrix.

4. What is scanning in keyboard and what is scan time?
The process of sending a zero to each row of a keyboard matrix and reading the columns for key actuation is called scanning. The scan time is the time taken by the processor to scan all the rows one by one starting from first row and coming back to the first row again.

5. What is the data and address size in 8086?
The 8086 can operate on either 8-bit or 16-bit data. The 8086 uses 20 bit address to access memory and 16-bit address to access 1/0 devices.

6. Explain the function of M/IO in 8086.
The signal M/IO is used to differentiate memory address and 1/0 address When the processor is accessing memory locations MI 10 is asserted high and when it is accessing 1/0 mapped devices it is asserted low.

7. Write the flags of 8086.
The 8086 has nine flags and they are
1. Carry Flag (CF) 2. Overflow Flag (OF) 3. Parity Flag (PF) 4. Trace Flag (TF)
5. Auxiliary carries Flag (AF) 6. Interrupt Flag (IF) 7. Zero Flag (ZF) 8. Direction Flag (DF)
9. Sign Flag (SF)

8. What are the interrupts of 8086?
The interrupts of 8085 are INTR and NMI. The INTR is general maskable interrupt and NMI is nonmaskable
interrupt.

9. How clock signal is generated in 8086? What is the maximum internal clock frequency of 8086?
The 8086 does not have on-chip clock generation circuit. Hence the clock generator chip, 8284 is connected to the CLK pin of8086. The clock signal supplied by 8284 is divided by three for internal use. The maximum internal clock frequency of8086 is 5MHz.

10. Write the special functions carried by the general purpose registers of 8086.
The special functions carried by the registers of 8086 are the following. Register Special function

  1. AX 16-bit Accumulator
  2.  AL 8-bit Accumulator
  3.  BX Base Register
  4.  CX Count Register
  5.  DX .Data Register

11. What is pipelined architecture?
In pipelined architecture the processor will have number of functional units and the execution time of functional units is overlapped. Each functional unit works independently most of the time.

12. What are the functional units available in 8086 architecture?
The bus interface unit and execution unit are the two functional units available in 8086 architecture.

13. List the segment registers of 8086.
The segment registers of 8086 are Code segment, Data segment, Stack segment and Extra segment registers.

14. Define machine cycle.
Machine cycle is defined as the time required to complete one operation of accessing memory, I/O, or acknowledging an external request. This cycle may consist of three to six T-states.

15. Define T-State.
T-State is defined as one subdivision of the operation performed in one clock period. These subdivisions are internal states synchronized with the system clock, and each T-State is precisely equal to one clock period.

16. List the components of microprocessor (single board microcomputer) based system
The microprocessor based system consist of microprocessor as CPU, semiconductor memories like EPROM and RAM, input device, output device and interfacing devices.

17. What are the internal devices of a typical DAC?
The internal devices of a DAC are R/2R resistive network, an internal latch and current to voltage converting amplifier.

18. What is settling or conversion time in DAC?
The time taken by the DAC to convert a given digital data to corresponding analog signal is called conversion time.

19. How single stepping can be done in 8086?
By setting the Trace Flag (TF) the 8086 goes to single-step mode. In this mode, after the execution of each instruction s 8086 generates an internal interrupt and by writing some interrupt service routine we can display the content of desired registers and memory locations. So it is useful for debugging the program.

20. Differentiate between absolute and linear select coding
Absolute decoding Linear decoding All higher address lines are defined to select the memory or I/O device Few higher address lines are decoded to select the memory or I/O device More h/w is required to design decoding logic Hardware required to design decoding logic is less Higher cost for decoding circuit Less cost for decoding circuit No multiple address Has a disadvantage of multiple addressing Used in large systems Used in small systems