The document discusses the different addressing modes in the 8051 microcontroller, including register, direct, register indirect, immediate, implied/register specific, and indexed addressing modes. It provides examples of instructions using each addressing mode and describes how registers, memory addresses, and immediate data values can be accessed. The 8051 has six working registers that can be selected from two register banks, and it allows access to on-chip RAM, SFR, and program memory using various addressing modes.

2. In 8051 There are six types of addressing modes.
 Register AddressingMode
 Direct AddressingMode
 Register IndirectAddressing Mode
 Immediate AddressingMode
 Implied/Register Specfic AddressingMode
 Indexed AddressingMode

3.  The register addressing instruction involves
information transfer between registers
 The 8051 can access eight ‘’working registers’’(R0-
R7).
 Three bit code within the instruction selects one of
the eight registers from the selected register bank.
 The programmer can select a register bank by
modifying bits 4 and 3 in the PSW.

4.  Example: add the content of register r3 and r4 from
bank 2.
 step 1: MOV PSW
 step 2:MOV A, R3
MOV A, R4

5.  Can access any on chip variable and hardware
register.(RAM and SF register).
 This mode allows you to specify the operand by
giving its actual memory address.
 the MSB of the address decides whether it is a
location within in the chip RAM(MSB=0) or in
SFR.(MSB=1).
 Example: MOV A,50H
ADD A, 51H

6.  addressing mode R0 and R1 of each register bank
can be used as an index or pointer register.
 R0 and R1 point to the contents in the RAM.
 the instruction with indirect addressing uses the@
sign.
 Example: MOV A , @R0
ADD A ,@R1

7.  In this Immediate Addressing Mode, the data is
provided in the instruction itself.
 The data is provided immediately after the opcode.
 The sign # indicates it is a immediate addressing
mode.
 Example: MOV A ,#52

8.  Inherent in the instruction, these refers to a specific
register such as accumulator or DPTR.
 In the implied addressing mode, there will be a
single operand.
 These types of instruction can work on specific
registers only.
 Example: RLA , SWAPA
 These are 1- byte instruction. The first one is used
to rotate the A register content to the Left. The
second one is used to swap the nibbles in A.

9.  Only program memory can be accessed in the
index addressing.
 Either DPTR or PC can be used as an index.
 Example: MOVCA, @A+PC;
MOVCA, @A+DPTR;
The C in MOVC instruction refers to code byte. For
the first instruction, let us consider A holds 30H. And
the PC value is1125H. The contents of program
memory location 1155H (30H + 1125H) are moved to
register A.

10.  Comparison b/w MC and MP
 Features of 8051
 Architecture
 Pin configuration
 Memory organization(external data and program)
 Addressing modes

11.  8051 microcontrollers are manufactured by which of the following
companies?
a) Atmel
b) Philips
c) Intel
d) All of the mentioned
 Unlike microprocessors, microcontrollers make use of batteries
because they have:
a) high power dissipation
b) low power consumption
c) low voltage consumption
d) low current consumption
 The internal RAM memory of the 8051 is:
A. 32 bytes
B. 64 bytes
C. 128 bytes
D. 256 bytes

12.  The 8051 has ________ 16-bit counter/timers.
A. 1 B. 2 C. 3 D. 4
 Microcontrollers often have:
A. CPUs
B. RAM
C. ROM
D. all of the above