Explore topic-wise InterviewSolutions in Current Affairs.

Register PC can hold 16- bit of address number.

Assembly language instructions like ADD and MOV are statements called directives.

Practice Assembly Language (PAL) Register can hold code address from 0000H to FFFFH (64K).

The mnemonic for immediate data is hash (#).

The mnemonic for loading decimal value 66 into R3 is MOV R3, #66.

Operational code (op code) is the short form of expressing the instruction. It consists of mnemonic and operands.

The meaning of MOV DPTR, #1246H is to load 16 bit number (1246H) immediately into register DPTR.

The meaning of MOV A, #22H is to load value 22H into accumulator A.

Copy the contents of register A(Accomulator) to Register 5.

The meaning of MOV A, @R1 is to copy the contents of RAM location whose address is stored in R1 into accumulator A.

The content of R0 is moved (copied) to register A (accumulator).

MOV opcode transfers data within the 8051 memory. MOV A, R1; MOV R0,22H; MOV A, #54H; MOV R2, #40.

1. Eight-bit CPU with registers A (Accumulator) and B.
2. Sixteen-bit program counter (PC) and data pointer(DPTR)
3. Eight-bit program status word (PSW)
4. Eight-bit stack pointer(SP)
5. Internal ROM or EPROM (8751) of 4k bytes
6. Internal RAM of 128 bytes :

(a) Four register banks, each containing eight registers

(b) Sixteen bytes, which may be addressed at the bit level

(c) Eight bytes of general purpose registers

7. Four 8-bit I/O ports (P0-P3)
8. Two 16-bit timer/counter TO and T1
9. Full duplex serial data receiver/ transmitter : SBUF
10. Control register: TCON, TMOD, SCON, PCON, IP and IE
11. Two external and two internal interrupt sources
12. Oscillator and clock circuits

Microcontroller 8051 has six(6) interrupt sources.

The register A is used to store the data temporarily and also to hold the result of arithmetic and logical instructions.

The memory is divided into Internal RAM, Internal SFR, External RAM, internal and External ROM.

i). Operating speed:

(a) DC – 20 MHz oscillator/clock input

(b) DC – 200 ns instruction cycle

ii). Flash memory size:

(a) 100,000 write Flash endurance

(b) 1,000,000 write EEPROM endurance

(c) Flash/Data EEPROM retention: > 40 years

iii). No. of pins of 16F877: 28 pins

Register R stores numbers temporarily.

MOV A, #34h
MOV 0F0, #3Fh
ADD A, 0F0
LCALL 0003h

The different programs required ALPs converted into code memory bit charges are:

a). An operating system program, which controls the operation of the personal computer used for the entire programming process. DOS is the operating system program used by many PCs. Windows is another.

b). A word processing, often called a text editor program. Programs in assembly language mnemonics are written using the text editor and stored on a disk as files that, normally, end in the extension asm. The asm files are intended for the use of another program called the assembler programs. Any text editor that can produce an ASCII (text) file is suitable for writing assembly language, asm files.

c). An assembler program, which takes the. asm assembly language program file and converts it to a machine code, obj file. The assembler converts the ASCII mnemonic text file into an. obj file that contains machine code instructions to the CPU, in binary form.

d). A testing program, which lets you run and test your program under controlled conditions. Testing your program is the most important step of the programming process. To be able to test program one must be able to execute each instruction and see the results. Utility programs that allow the user to test programs are called debuggers or simulators.

FFH is the largest value that can be moved into an 8 bit register.

MOV A, #1Eh
ADD A, #1Ch
MOV R6, A
LCALL 0003h

PIC microcontrollers has working voltage range of 2.0V to 5.5V.

PIC microcontrollers are a family of microcontroller chips produced by microchip technology.

PIC is Peripheral Interface Controller.

PIC microcontrollers has one accumulator.

The steps to create a program are:

(i) Program editor is used to type in the program. The editor must be able to produce ASCII file for many assembler and will have the extension “.asm” or “src”.

(ii) Assembler on receiving the file in “.asm” form converts the instructions into steps to creat a program machine code. Assembler will produce an object file “.obj” and list file “.1st”.

(iii) Linker program links one or more object files and produce an absolute object file “.abs”.

(iv) The “.abs” file is fed to object to hex converter(OH) and create an extension “.hex” and is ready to run ROM.

Address in memory that is used by the CPU to read or write is called data address.

Static Random Access Memory.

ROM is called non volatile because it does not depend on electrical power to store the numbers.

RAM is called volatile because it depends on electrical power to store the numbers, when power is OFF it loses its information.

Clock circuit generates the internal clock pulses and all the internal operations are synchronised with this pulse.

It is an electronic circuit, which breaks in the normal flow of system or routine and flow can be resumed from that point at a later time.

Logical operations like AND, OR, XOR, complement, rotate are performed by these instructions. One of the operand is always register A.

These instructions perform several basic arithmetic operations. After execution, the result is stored in the first operand. 8 bit addition, subtraction, multiplication, increment-decrement instructions can be performed in 8051.

Example:
ADDA, Rn
ADDA, #8 bit data
ADDC A, Direct
ADDC A, Rn
ADDC A, @Ri
ADDC A, #8 bit data
SUBB A, Rn
SUBB A, Direct
SUBB A, @Ri
SUBB A, #8 bit data
INC A
INC Rn
INC Direct
INC @Ri
DEC A
DEC Rn
DEC Direct
DEC @Ri
INC DPTR
MUL A B
DIVA B
DA A

Various arithmetic operations are carried out in this group of instructions. ADD, SUB, INC, DEC, MUL, DIV are the basic operations used.

The call instruction temporarily changes the contents of program counter to allow another part of the program to run either conditionally or unconditionally.

In data transfer instructions, data is moved(copied) from the source to destination. Most of the instructions in this group does not affect the PSW flags. MOV, PUSH, POP and XCH are the commonly used instructions in this group.

In PIC16F877 microcontrollers 8k ROM memory in flash technology upto 105 times chip can be reprogrammed.

Maximum operating frequency of PIC16F877 is 20MHz.

Assembly language is a series of lines of assembly language instructions consisting of mnemonics, one or two operands. The four fields of assembly language are: label, mnemonic, operand, comment.

Machine language is one in which information is available only in binary form.

Assembly language fills the gap between low level machine language and high level language. It is written in instruction mnemonics.

MOV R2, #15H

PAL contains three internal registers:

Register A: Performs all operations in the CPU. 

Register B: Stores numbers temporarily.

Register PC: Holds the address of the next instruction to be executed in code memory. 

Register A and R can hold 8 bits of binary data and register PC can hold a 16-bit address number. PAL is called an 8-bit computer because the working registers A and R can hold a 1-byte number. PAL register PC limits the number of code byte addresses to 64k because it can hold code address from address 0000H to address FFFFH.

The content of register R2 is added with the content of accumulator and the the sum is stored in the accumulator.

The CPU can store data may be in registers, memory or in an external source. The ways by which these data source address are specified are called addressing modes. These are necessary because, the data can be accessed using any one of the modes.

In direct addressing mode 128 bytes of internal RAM and SFRs may be addressed directly using single byte address assigned to each RAM location and each SFR.

There are four addressing modes in 8051

(i) Immediate addressing mode

(ii) Register addressing mode

(iii) Direct addressing mode

(iv) Indirect addressing mode