DMI COLLEGE OF ENGINEERING EC6504 - Microprocessor and Microcontroller UNIT I THE 8086 MICROPROCESSOR 1. What are different data transfer schemes? The different data transfer schemes are [A/M 12] 2. How is clock signal generated in 8086? What is the maximum internal clock frequency of 8086? [N/D 12] The 8086 does not have on-chip clock generation circuit. Hence the clock generator chip, 8284 generates the CLK signal. The clock signal supplied by 8284 is divided by three for internal use. The maximum internal clock frequency of 8086 is 5 MHz. 3. Write the function of queue status lines QS0 and QS1 in 8086 microprocessor. The function of queue status lines QS0 and QS1 in 8086 microprocessor is to indicate the activity in the queue during previous clock cycle. [N/D 12] 4. What is a Microprocessor? What is the difference between Microprocessor and CPU? Department of Electronics and Communication Engineering 1
A microprocessor is a multipurpose, programmable logic device that accepts binary data as input, processes data according to the instructions and provides output in binary form. It reads binary instructions from a storage device called memory. The CPU is the unit that includes ALU and control unit. Apart from processing the data, the CPU controls the entire system functioning. Usually, a microprocessor will be the CPU of a system and it is called the brain of the computer. [N/D 11] 5. Why the program counter and the stack pointer registers are16 bits? [N/D 11] Program Counter (PC) and Stack Pointer (SP) are used to hold 16-bit memory addresses. PC stores the 16-bit memory address of the next instruction to be fetched. SP points to the beginning of stack memory. SP can be used to temporarily store the 16-bit memory address as well as data. So, PC and SP are 16-bit registers. 6. What are Tristate devices? A tri-state device is a digital device. The device is in the high state, the low state, or in a high impedance state to prevent loading. This allows multiple circuits to share the same output line or lines. [N/D 10] 7. Draw the flag register for 8086. The flag register of 8086 is given below: Conditional Flags: Department of Electronics and Communication Engineering 2
CF - Carry Flag PF - Parity Flag AF - Auxiliary Carry Flag ZF - Zero Flag SF - Sign Flag OF - Overflow Flag Control Flags: TF Single step Trap Flag IF Interrupt Enable Flag DF String Direction Flag 8. What is the purpose of Bus Interface Unit? The purpose of BIU is to interface 8086 with the outside world. It provides a 16-bit bidirectional data bus and 20-bit address bus. This unit is responsible for performing external bus operations. Functions 1. It fetches instruction from memory. 2. It reads data from port/memory. 3. It writes data into port/memory. 4. It supports instruction queuing. 5. It provides address relocation facility 9. Write the size of the data bus and address bus of 8086? The size of data bus and address bus of 8086 are 16-bit and 20-bit respectively. 10. What is the function of an accumulator? Accumulator is a tri-state eight bit register. It is extensively used in arithmetic, logic, load and store operations, as well as in input/output (I/O) operations. The result of arithmetic and logical operations is stored in the register A. Hence, it is also identified as accumulator. 11. What is the clock frequency of 8086? The maximum internal clock frequency of 8086 is 5 MHz. 12. What is memory segmentation? Department of Electronics and Communication Engineering 3
Memory segmentation is dividing the linear memory space into chunks called segments. 8086 segmented memory system has four segments Code segment, Data segment, Extra segment, and Stack segment. 13. What is pipelining? In 8086, to speed up the execution of program, the instructions fetching and execution of instructions are overlapped each other. This technique is known as pipelining. In pipelining, when the n th instruction is executed, the n+1 th instruction is fetched and thus the processing speed is increased. 14. What is meant by physical addressing in 8086? Physical addressing is used to address 1MB memory of 8086. The 8086 memory address is 20 bits but all the registers used for memory calculation are of 16 bit length. The 20 bit physical address is computed by summing the contents of the segment register (shifted left by 4 bits) and an effective (offset) address. The segment register holds the upper 16 bits of the 20 bit memory address. The effective address represents the offset from the starting address of the segment Eg: (CS x 10H ) + IP = Physical address CS is shifted left by 4 bit and summed with IP (offset) to compute physical address. 15. Define Segment Override Prefix The segment override prefix allows the programmer to deviate from the default segment. It is an additional 8-bit code selects the alternate segment register. The code byte for the segment override prefix as the format 001XX110. The XX represents 2 bits which are as follow: ES = 00, CS = 01, SS = 10, DS = 11. 16. How is the memory segment accessed by 8086 microprocessor? [A/M 11] The memory segment accessed by 8086 microprocessor is identified by the status of the status bits S3, S4. The Status bits S3, S4 when decoded, indicate the type of operation (memory access) being performed and the segment register being used. Department of Electronics and Communication Engineering 4
UNIT II 8086 SYSTEM BUS STRUCTURE 1. What is the function of the signal in 8086? BHE signal means Bus High Enable signal. The BHE signal is made low when there is some read or write operation is carried out. ie. When ever the data bus of the system is busy i.e. whenever there is some data transfer then the BHE signal is made low. 2. State the significance of LOCK signal in 8086. If 8086 is working at maximum mode, there are multiprocessors are present. If the system bus is given to a processor then the LOCK signal is made low. That means the system bus is busy and it cannot be given of any other processors. After the use of the system bus again the LOCK signal is made high. That means it is ready to give the system bus to any processor. 3. What are the functions of bus interface unit (BIU) in 8086? (a) Fetch instructions from memory. (b) Fetch data from memory and I/O ports. (c) Write data to memory and I/O ports. (d) To communicate with outside world. (e) Provide external bus operations and bus control signals. 4. What are the two modes of operations present in 8086? i. Minimum mode (or) Uniprocessor system ii. Maximum mode (or) Multiprocessor system 5. What is multiprogramming? If more than one process is carried out at the same time, then it is known as Department of Electronics and Communication Engineering 5
multiprogramming. Another definition is the interleaving of CPU and I/O operations among several programs is called multiprogramming. To improve the utilization of CPU and I/O devices, we are designing to process a set of independent programs concurrently by a single CPU. This technique is known as multiprogramming 6. What is the importance of? INTA Interrupt Acknowledge generated by the microprocessor in response to INTR. Causes the interrupt vector to be put onto the data bus. 7. Under what conditions can bus contention occurs?how does a tri-state buffer help avoid this problem? Bus contention occurs when two outputs attempting to control the same line. It can be avoided by tri-state buffer can be turned off 8. List the chips and their function required to design maximum mode single-processor 8086 CPU module. 1.8284A clock generator 2.8288 bus controller 3.8282/83 bus duffers 4.8286/87 address latches 9. What are the advantages of multiprocessor system? High level performance can be attained when parallel processing. Robustness can be improved by isolating system functions. 10. What are the problems occurred in multiprocessor system? 1. Bus contention 2. Interprocess communication 3. Resource sharing 11. What is Coprocessor? Department of Electronics and Communication Engineering 6
The coprocessor is a processor which specially designed for processor to work under the control of the processor and support special processing capabilities. Example : 8087 which has numeric processing capability and works under 8086. 12. What are the basic multiprocessor configurations? 1. Coprocessor configuration 2. Closely Coupled configuration 13. What are the schemes for establishing priority in order to resolve bus arbitration problem? There are three basic bus access control and arbitration schemes 1. Daisy Chaining 2. Independent Request 3. Polling 14. Compare closely coupled and loosely coupled configurations. Closely coupled Loosely coupled 1. Single CPU is used 1. Multiple CPU modules are used 2. It has local bus only 2. It has local as well system bus 3. No system memory or IO 3. It has system memory and IO, shared among CPU modules Department of Electronics and Communication Engineering 7
4. No bus arbitration logic required 4. Bus arbitration logic required 15. What is mean by loosely coupled multiprocessor system? In loosely coupled multiprocessor system, each processor has a set of Input/output devices and a large memory, where it accesses most of the instructions and data. 16. Write the advantages of loosely coupled system over tightly coupled systems? 1. More number of CPUs can be added in a loosely coupled system to improve the system performance 2. The system structure is modular and hence easy to maintain and troubleshoot. 3. A fault in a single module does not lead to a complete system breakdown. Department of Electronics and Communication Engineering 8
UNIT III I/O INTERFACING 1. What are the modes of operation supported by 8255? The modes of operations supported by 8255 are: 1. I/O Mode (Input / Output mode) a) Mode 0 Simple I/O b) Mode 1 Handshaking or Strobed I/O mode c) Mode 2 Strobed bidirectional I/O Mode 2. BSR Mode (Bit set / reset mode ) 2. What are the enhanced features of 8254 Programmable Interval Timer compared with 8253? [N/D 12] The enhanced features of 8254 Programmable Interval Timer compared with 8253 are: 1. Operating frequency 0 10 MHz. 2. Uses H-MOS technology. 3. Read-Back command is available. 4. Reads and writes of the same counter can be interleaved. 3. What are the functions of the scan section in 8279? [A/M 11] The functions of scan counter in scan section are: 1. To scan the key matrix (keyboard) 2. To refresh the display In encoded mode scan counter provides a binary count from 0000 to 1111 on four scan lines (SC 3 SC 0) with active high outputs. In decoded mode scan counter decodes least significant 2 bits of binary counts and provides 4 possible combinations on scan lines (SC3 SC0): 1110, 1101, 1011, and 0111. Department of Electronics and Communication Engineering 9
4. To which port of the CPU is CRT monitor and printer connected? [N/D 11] The CPU is connected to CRT monitor through serial port using RS232 interface. The printer is connected to CPU through serial interface (serial port) using RS232 interface or parallel interface through parallel port (8255). 5. What is the operating frequency of 8279? The required internal operating frequency of 8279 is 100 KHz to a maximum of 3 MHz. 6. What is Key debounce? Key debounce is the minimum time that the microprocessor must wait for the key to reach steady state when a key is pressed. Mechanical switches are used as keys in most of the keyboards. When a key is pressed, the contact bounces back and forth and settles down only after a small time delay (about 20 ms). 7. Compare the features of A/D converter with D/A converter. [N/D 11] A/D converter D/A converter 1 An analog-to-digital converter (abbreviated A digital-to-analog ADC, A/D or A to D) converts a continuous converter (abbreviated physical quantity (usually voltage) to an equivalent digital value. DAC, D/A) translates digital information into equivalent Analog quantity (voltage or current). 2 The basic techniques include ramp, The basic technique integrating ramp, successive approximation. include decoder resistance network. 8. Define Resolution of ADC [M/J 12] Resolution is defined as the minimum change in voltage (input) required to guarantee a change in the output code level. The resolution Q of the ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the Department of Electronics and Communication Engineering 10
number of discrete values. It is expressed in volts. EFSR is the full scale voltage range. M is the number of bits in an M bit ADC. 9. What is the function of sample and hold circuit? [A/M 11][N/D 10] [M/J 12] A sample and hold circuit is a circuit which samples an input signal, and holds on to its last sampled value until the input is sampled again. Sample and hold circuits are commonly used in analog to digital converter, communication circuits, PWM circuits, etc. 10. List out the major functions performed by CRT interface. [A/M 11] The major functions performed by CRT interface are: 1. CRT terminals work on RS232 C interface. 2. CRT interface transmits and receives the binary data serially with fixed baud rate. 3. CRT interface has three terminals TXD, RXD, GND. 4. TXD is used for data transmission from CRT to microprocessor. 5. RXD is used for data transmission from microprocessor to CRT. 6. GND is used for common ground. 11. What are the functional types used in control words of 8251A? The control words of 8251A are divided into two functional types. 1. Mode Instruction control word 2. Command Instruction control word Mode Instruction control word :-This defines the general operational characteristics of 8251A. 2.Command Instruction control word:-the command instruction controls the actual operations of the selected format like enable transmit/receive, error reset and modem control. 12. Write the features of mode 0 in 8255? 1. Two 8-bit ports (port A and port B) and two 4-bit ports (port C upper and lower) are available. The two 4-bit ports can be combined used as a third 8-bit port. 2. Any port can be used as an input or output port. 3.Output ports are latched. Input ports are not latched. 4. A maximum of four ports are available so that overall 16 I/O configurations are possible. Department of Electronics and Communication Engineering 11
13. What are the features used mode 1 in 8255? Two groups group A and group B are available for strobed data transfer. 1. Each group contains one 8-bit data I/O port and one 4-bit control/data port. 2. The 8-bit data port can be either used as input or output port. The inputs and outputs both are latched. 3. Out of 8-bit port C, PC0-PC2 is used to generate control signals for port B and PC3=PC5 are used to generate control signals for port A. The lines PC6, PC7 may be used as independent data lines. 14. What is the function of mode set register in 8257? The mode set register is used for programming the 8257 as per the requirements of the system. The function of the mode set register is to enable the DMA channels individually and also to set the various modes of operation. Department of Electronics and Communication Engineering 12
UNIT IV MICROCONTROLLER 1. What is a microcontroller? Microcontroller is a device which contains the microprocessor with integrated peripherals like memory, serial ports, parallel ports, timer/counter, interrupt controller, data acquisition interfaces like ADC, DAC. 2. What happens in power down mode of 8051 microcontroller? [M/J 13 ][A/M 11 ] The microcontroller enters power down mode by setting the PD bit to 1. The following happens in power down mode of 8051 microcontroller: a) The internal clock to the entire microcontroller is stopped. However, the program is not dead. b) Vcc can be reduced to as low as 2V in power down mode. c) The internal RAM gets it back up supply from RST/VPD pin. d) Port values are not changed /overwritten in power down mode. 3. What is the size of memory systems used in 8051 microcontroller? [N/D 12] The size of the memory systems in 8051 microcontroller are: External program memory (ROM) 64 Kbytes External data memory (RAM) 64 Kbytes Internal ROM 4 Kbytes Internal RAM 128 bytes Department of Electronics and Communication Engineering 13
4. What is the function of RS1 and RS0 bits in the flag register of Intel 8051 microcontroller? The function of RS1 and RS0 bits in the flag register is to select the register bank. RS1, RS0 Register bank select bits RS1 RS0 Bank Selection Address 0 0 Bank 0 00h 07h 0 1 Bank 1 08h 0Fh 1 0 Bank 2 10h 17h 1 1 Bank 3 18h 1Fh 5. List out the applications of 8051 microcontroller. The applications of 8051 microcontroller are Control applications: Office automation, home automation and industrial automation. Embedded applications: Since, it is single chip controller, 8051 microcontrollers are much useful in all embedded applications like real time, wireless modes. Network applications: In the area of wireless networking, including LAN, MAN, and WAN. Common applications: Used in the measurement of frequency, reactance, voltage, current, resistance, temperature, strain management, etc. It is also used in delay subroutine, LED display, relays, and for interfacing with other electronic components. 6. List out the advantages of general purpose registers / register banks. The advantages of general purpose registers are: a) Used by programmers Department of Electronics and Communication Engineering 14
b) Default power setup c) Less processing time 7. What is PSW? PSW (Program Status Word register) is an 8 bit register that contains the status of the program information. PSW consists of 4 types of flags namely carry, auxiliary carry, overflow and parity flag. PSW is bit addressable register. It is used to select the register bank (RS1 and RS0). C AC F0 RS1 RS2 OV - P 8. What is the size of internal RAM and ROM of 8051? The size of internal RAM and ROM of 8051 microcontroller are: Internal ROM 4 Kbytes Internal RAM 128 bytes 9. List out the flags available in 8051. The flags available in 8051 are: Four mathematical flags, Carry (CY), Auxiliary Carry (AC), Overflow Flag (OF) and Parity flag (P) specified in PSW register. Two general purpose flags GF0 and GF1 in the PCON register. 10. What is meant by Power On Reset in 8051? Power On Reset in 8051 will reset the microcontroller and terminate all activities. It also causes all values in the register to be lost. The reset pin in 8051 is pin 9. It is normally low. Upon applying high pulse to this pin, power on reset is activated. 11. What is the need for bitwise instructions in microcontroller? [M/J 12] Bitwise instructions are needed in microcontroller for the following reasons: 1. Sometimes only 1 or 2 bits of the port are to be accessed instead of entire 8 bits without altering the rest of the bits in the port. Department of Electronics and Communication Engineering 15
2. It requires discrete input and output bits, to control or detect the logic state of devices like switches, LEDs, LCD displays and sensors for data such as temperature, humidity, light level etc. 3. Since, microcontrollers are used in automatically controlled products and devices, such as appliances, toys and other embedded systems. 12. What are the operand types used in 8051 microcontroller? [N/D 12] The different operand types used in 8051 microcontroller are: Immediate operand a) Register b) Memory 13. What are the different ways of operand addressing in 8051? [A/M 11] The different ways of operand addressing in 8051 are: a) Immediate addressing b) Register addressing c) Direct addressing d) Indirect addressing e) Relative addressing f) Index addressing 14. What are the advantages of the register indirect addressing mode in 8051 microcontroller? [N/D 10] The advantages of the register indirect addressing mode in 8051 microcontroller are: a. It makes accessing data dynamic rather than static as in the case of direct addressing mode. b. Looping is possible in register indirect addressing mode. Department of Electronics and Communication Engineering 16
15. Write an 8051 program to monitor P1 continuously. It should get out of the monitoring only if P1 = 63H. [N/D 10] LABEL: LABEL HERE: MOV P1, # 0FFh MOV A, P1 CJNE A, # 63, SJMP HERE 16. List out the special function registers used for port operation in 8051? [M/J 12 ] The special function registers used for port operation in 8051 are P0, P1, P2, and P3. Each port are 8 bit wide which are bit addressable i.e. each bit can be set or reset by the bit instructions (SETB for high, CLR for low) independently. The address of 1. Port 0 is 80 2. Port 1 is 90 3. Port 2 is A0 4. Port 3 is B0 17. What are the hardware and software interrupts of 8051 μc? Write its vector address. [N/D 11 ] The hardware and software interrupts of 8051 μc are: External hardware interrupt 0 (INT0) 0003H External hardware interrupt 1 (INT1) 0013H Timer 0 interrupt (TF0) 000BH Timer 1 interrupt (TF1) 001BH Serial port interrupt (RI or TI) 0023H 18. How many ports are bit addressable in 8051 microcontroller? [N/D 11] All the ports (Port 0 to Port 3) are bit addressable in 8051 Microcontroller. 19. List out the timers available in 8051. Department of Electronics and Communication Engineering 17
The timers available in 8051 are Timer 0 (T0) 16 bit timer / counter Timer 1 (T1) 16 bit timer / counter These two timers can be configured either as timers or event counters. They can be split into two byte register namely TL0, TH0, TL1, and TH1. 20. What is the function of SCON register? The SCON register is an 8 bit register used to program the start bit, stop bit, and data bit of the data framing. The following format describes the various bits D7 D6 D5 D4 D3 D2 D1 D0 SM0 SM1 SM2 REN TB8 RB8 TI RI SM0 SM1 MODE 0 0 Serial Mode 0 0 1 Serial Mode 1 1 0 Serial Mode 2 1 1 Serial Mode 3 SM2: 1 for multiprocessor communication 0 for single processor REN: SET/CLEAR by software to enable or disable reception TB8: Transmit bit for serial mode 2 and 3 RB8: Receive bit for serial mode 2 and 3 21. What is the function of PCON register? The function of PCON register is to select the power modes in 8051.The configuration Department of Electronics and Communication Engineering 18
of (PCON) power control register is shown below: SMOD: Serial baud rate modify bit GF1 : General purpose user flag bit 1 GF0 : General purpose user flag bit 0 PD : Power down bit IDL : Idle mode bit UNIT V INTERFACING MICROCONTROLLER 1. List the modes of Timer in 8051. The modes of timer in 8051 are chosen with the help of two bits,viz., M0 & M1 in TMOD register. M1 MO Mode Description of Timer 0 0 0 13-bit timer 0 1 1 16-bit timer 1 0 2 8-bit timer with auto reload 1 1 3 Split timer 2. What is the significance of C/T bit in TMOD register of 8051? The C/T bit in the TMOD register is a selector bit for the type of operation to perform in the timer register. HIGH in that bit indicates Counter operation and LOW in that bit indicates Timer operation. 0 Timer Operation 1 Counter Operation 3. What is the significance of TRx bit in TCON register of 8051? TRx bit in the TCON register is used to Start / Stop the timer register for both timer and counter operation, by setting that bit with value 1 or 0. Department of Electronics and Communication Engineering 19
4. Explain the Timer operation of 8051. In this mode, the timer register is used to generate the time delay using theclock signal applied to the processor.an initial count is loaded in the timer register. When the timer is started, thetimer register content gets incremented after every machine cycle. When thetimer register crosses (i.e., overflows) the count FFFFH and goes to 0000H,the timer overflow flag in TCON register becomes set.hence, by loading appropriate value in the timer register, a specific timedelay can be generated using timer. One machine cycle consists of 12 clocksignal periods and the delay is equal to count value loaded * time period of one machine cycle 5. List the Interrupt sources in 8051. The Six Interrupt sources in 8051 are RESET INT0, INT1 TF0, TF1 SPI (TI/RI) 6. What are the types of serial communication? The serial communication can be, Synchronous (continuous) Iso-Synchronous (with regular time intervals) Asynchronous (with irregular time intervals) 7. Define Baud rate. It is the speed of serial data transfer, expressed in bits/sec.the standard baud rates are110, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 8. Explain the operating mode2 of 8051 serial ports. In this mode 11 bits are transmitted(through TXD)or received (through RXD):a start bit(0), 8 data bits(lsb first),a programmable 9th data bit,& a stop bit(1).on transmit the 9th data bit (TB* in SCON)can be assigned the value of 0 or 1.Or for eg:, the parity bit(p, in the PSW)could be moved into TB8.On receive the 9th d ata bit go in to the RB8 in Special Function Register SCON, while the stop bit is ignored. The baud rate is programmable to Department of Electronics and Communication Engineering 20
either 1/32 or 1/64 the oscillator frequency. 9. Explain the operating mode0 of 8051 serial ports. In this mode serial enters &exits through RXD, TXD outputs the shift clock.8 bits are transmitted/received:8 data bits(lsb first).the baud rate is fixed at 1/12 the oscillator frequency. 10. What are the tasks involved in keyboard interfacing? The task involved in keyboard interfacing are sensing a keyboard interfacing are sensing a key actuation, de bouncing 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. 11. How a keyboard matrix is formed in keyboard interface? The return lines RL0 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. 12. 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. 13. What is scanning in display and what is the scan time? In display devices the process of sending display codes to 7-segment LED S to display the led s one by one is called scanning. The scan time is the time taken to display all the 7- segment LED S one by one, starting from first LED and coming back to the first LED again. Department of Electronics and Communication Engineering 21
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