Important Short Questions and Answers: 8051 Micro Controller

MICROCONTROLLERS 8051

1. What is mean by microcontroller?

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 is called microcontroller.

2. Explain DJNZ instruction of Intel 8051 microcontroller?

ü DJNZ Rn, rel Decrement the content of the register Rn and jump if not zero.

ü DJNZ direct, rel Decrement the content of direct 8- bit address and jump if not zero.

3. State the function of RS1 and RS0 bits in the flag register of Intel 8051 microcontroller?

RS1, RS0- Register bank select bits

RS1, RS0- Bank

Bank 0

Bank 1

Bank 2

Bank 3

4. Give the alternate functions for the port pins of port3?

RD WR T1 T0

INT 1 INT 0 TXD RXD

ü RD – Read data control output

ü WR – Write data control output

ü T1 – Timer / counter 1 external input or test pin T0 – Timer / counter 0 external input or test pin INT 1 – Interrupt 1 input pin

ü INT 0 – interrupt 0 input pin

ü TXD – Transmit data pin for serial port in UART mode

ü RXD – Receive data pin for serial port in UART mode

5. Specify the single instruction, which clears the most significant bit of B register of 8051, without affecting the remaining bits.

Single instruction, which clears the most significant bit of B register of 8051, without affecting the remaining bits, is CLR B.7.

6. Explain the function of the pins PSEN and EA of 8051.

PSEN: PSEN stands for program store enable. In 8051 based system in which an external

ROM holds the program code, this pin is connected to the OE pin of the ROM.

EA: EA stands for external access. When the EA pin is connected to Vcc, program fetched to address 0000H through 0FFFH are directed to the internal ROM and program fetches to addresses 1000H through FFFFH are directed to external ROM/EPROM. When the EA pin is grounded, all addresses fetched by program are directed to the external ROM/EPROM.

7. Explain the 16-bit registers DPTR and SP of 8051. DPTR:

DPTR stands for data pointer. DPTR consists of a high byte (DPH) and a low byte (DPL).

Its function is to hold a 16-bit address. It may be manipulated as a 16- bit data registers. It serves as a base register in indirect jumps, lookup table instructions and external data transfer.

SP:

SP stands for stack pointer. SP is a 8-bit wide register. It is incremented before data is stored during PUSH and CALL instructions. The stack array can reside anywhere in-chip RAM. The stack pointer is initiailsed to 07H after a reset. This causes the stack to begin at location. 08H.

8. Name the special functions registers available in 8051.

ü Accumulator

ü B Register

ü Stack pointer.

ü Data pointer

ü Interrupt priority control register.

ü Interrupt enable control register.

9. Explain the register IE format of 8051.

EA ET2 ES

ET1 EX1 ET0 EX0

EA- Enable all control bit.

ü ET2- Timer 2 interrupt enable bit. ES- Enable serial port control bit. ET1- Enable Timer1 control bit.

ü EX1-Enable external interrupt1 control bit. ET0-Enable Timer0 control bit.

ü EX0-Enable external interrupt0 control bit.

10. Compare Microprocessor and Microcontroller.

Microprocessor

1.       Microprocessor contains ALU, general register counter, clock timing

interrupt circuit.

2.       It has many instructions to move data and CPU.

3.       It has one or two bit handling instruction .

4.       Access times for memory and I/O Devices are more.

5.       Microprocessor based system requires more hardware

Microcontroller

1. Microcontroller contains the circuitry of Purpose microprocessor and in addition it has Circuit and Built-in ROM, RAM, I/O devices and counter.

2. It has many instructions to move between memory data between memory and CPU.

3. it has many bit handling instructions.

4. Less access times for built-in memory and I/O devices.

5. Microcontroller based system requires less hardware reducing PCB size and Increasing the reliability.

11. Name the five interrupt sources of 8051?

The interrupt are:

Vector address

ü External interrupt 0: IE0: 0003H

ü Timers interrupt 0: TF0: 000BH

ü External interrupt 1: IE1: 0013H

ü Timers interrupt 1: TF1:001BH Serial interrupt

ü Receive interrupt: RI: 0023H

ü Transmit interrupt: TI: 0023H

12.            Write a program to subtract the contents of RI of Bank0 from the contents of R0 0f Bank2.

MOV PSW, #10

MOV A, R0

MOV PSW, #00

SUBB A, R1

13. How the RS-232 serial bus is interrupt to 1TL logic device?

The RS-232 signal voltage level devices are not compatible with TTL logic levels. Hence for interfacing TTL devices to RS-232 serial bus, level converters are used. The popularly used level converters are MC 1488 & MC 1489 or MAX 232.

14. List some of the features of 8096 microcontroller.

ü The 8096 is a 16-bit microcontroller.

ü The 8096 is designed to use in application which require high speed calculations and fast I/O operation.

ü The high speed I/O section of an 8096 includes a 16-bit timer, a 16- bit counter, a 4 input programmable edge detector, 4 software timer and counter 6-output programmable events Generator.

ü It has 100 instructions, which can operate on bit, byte, word and double words.

15.            List the features of 8051 microcontroller?

The features are

ü Single supply +5 volt operation using HMOS technology.

ü 4096 bytes program memory on chip (not on 8031)

ü 128 data register banks

ü Four register mode, 16-bit timer/ counter.

ü Extensive Boolean processing capabilities.

ü 64 KB external RAM size

ü 32 bi-directional individually addressable I/O lines.

ü 8 bit CPU optimized for control applications.

16.            Explain the operating mode 0 of 8051 serial ports?

In this mode serial enters & exits through transmitted/received: 8 data bits (LSB first). frequency.

RXD, TXD outputs the shift clock 8 bits are The baud rate is fixed at 1/12 the oscillator

17. Explain the operating mode 0 of 8051 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 9^th data bit, & a stop bit (1).ON transmit the 9^th data bit (TB* in SCON) can be assigned the value of 0 or 1.

For eg: the parity bit (P, in the PSW) could be moved into TB8. On receive the 9^th data bit go in to the RS8 in Special Function Register SCON, while the stop bit is ignored. The baud rate is programmable to either 1/32, or 1/64 the oscillator frequency.

18. Explain the mode 3 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 9^th data bit, & a stop bit (1). In fact, Mode 3 is the same as Mode 2 in all respect except the baud rate. The baud rate in Mode 3 is variable.

In all the four modes, transmission is initiated by any instruction that uses SBUF as a destination register. Reception is initiated in Mode 0 by the condition RI=0 & REN=1. Reception is initiated in other modes by the incoming start bit if REn=1.

19.            List the addressing modes of 8051?

ü Direct addressing

ü Register addressing

ü Register indirect addressing

ü Implicit addressing

ü Immediate addressing

ü Index addressing

ü Bit addressing