Addressing modes of Microcontroller

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