Microprocessor
• Microprocessor is the CPU of a Microcomputer.
• It is the heart of the micro computer.
• Microprocessor or is a silicon chip that contains a CPU. In the world
of personal computers, the terms microprocessor and CPU are used
interchangeably.
• A microprocessor (sometimes abbreviated μP) is a digital electronic
component with miniaturized transistors on a single semiconductor
integrated circuit (IC).
• One or more microprocessors typically serve as a central processing
unit (CPU) in a computer system or handheld device.

Microprocessor
• Microprocessors made possible the advent of
the microcomputer.
• At the heart of all personal computers and most
working stations sits a microprocessor.
• Microprocessors also control the logic of almost
all digital devices, from clock radios to fuel-
injection systems for automobiles.

Microprocessor’s Characteristics
Three basic characteristics differentiate microprocessors:
• Instruction set: The set of instructions that the
microprocessor can execute.
• Bandwidth: The number of bits processed in a single
instruction.
• Clock speed: Given in megahertz (MHz), the clock speed
determines how many instructions per second the
processor can execute.

Microcontroller
A highly integrated chip that contains all the components comprising a
controller.
• Typically this includes a CPU, RAM, some form of ROM, I/O ports,
and timers.
• Unlike a general-purpose computer, which also includes all of these
components, a microcontroller is designed for a very specific task -
to control a particular system.
• A microcontroller differs from a microprocessor, which is a general-
purpose chip that is used to create a multi-function computer or
device and requires multiple chips to handle various tasks.
•.

• A microcontroller is meant to be more self-contained and
independent, and functions as a tiny, dedicated computer.
• The great advantage of microcontrollers, as opposed to using larger
microprocessors, is that the parts-count and design costs of the item
being controlled can be kept to a minimum.
• They are typically designed using CMOS (complementary metal oxide
semiconductor) technology, an efficient fabrication technique that
uses less power and is more immune to power spikes than other
techniques.
• Microcontrollers are sometimes called embedded microcontrollers,
which just means that they are part of an embedded system that is,
one part of a larger device or system

Controller
A device that controls the transfer of data from a computer
to a peripheral device and vice versa.
• For example, disk drives, display screens, keyboards and
printers all require controllers.
• In personal computers, the controllers are often single
chips.
• When you purchase a computer, it comes with all the
necessary controllers for standard components, such as
the display screen, keyboard, and disk drives.

Difference
MICRO PROCESSER
• It is a CPU
• Memory, I/O Ports to be
connected externally
MICRO CONTROLLER
• It is a single chip
• Consists Memory, I/O
ports

BUS: A shared group of wires used for
communicating signals among devices.
– address bus: the device and the location within the
device that is being accessed
– data bus: the data value being communicated
– control bus: describes the action on the address
and data buses
CPU: Core of the processor, where instructions are
executed
– High-level language: a = b + c
– Assembly language: add r1 r2 r3
– Machine language: 0001001010111010101

Memory: Where instructions (programs) and data
are stored
– Organized in arrays of locations (addresses), each
storing one byte (8 bits) in general
– A read operation to a particular location always
returns the last value stored in that location
I/O devices: Enable system to interact with the
world.
– Device interface (a.k.a. controller or adapter)
hardware connects actual device to bus
– The CPU views the I/O device registers just like
memory that can be accessed over the bus.
However, I/O registers are connected to external
wires, device control logic, etc.
– Reads may not return last value written
– Writes may have side effects

Big-Endian and Little-Endian Storage
When data types having a word size larger than the smallest
addressable unit are stored in memory the question arises,
“Is the least significant part of the word stored at the
lowest address (little Endian, little end first) or–
is the most significant part of the word stored at the
lowest address (big Endian, big end first)”?
Example: The hexadecimal 16-bit number ABCDH, stored at address 0:
AB CD
msb ... lsb
AB
CD0
1
AB
CD
0
1
Little
Endian
Big Endian

von Neumann architecture
• The von Neumann architecture is a design model for a stored-program
digital computer that uses a central processing unit (CPU) and a single
separate storage structure ("memory") to hold both instructions and data. It
is named after the mathematician and early computer scientist John von
Neumann. Such computers implement a universal Turing machine and have
a sequential architecture.
• A stored-program digital computer is one that keeps its programmed
instructions, as well as its data, in read-write, random-access memory
(RAM). Stored-program computers were an advancement over the program-
controlled computers of the 1940s, such as the Colossus and the ENIAC,
which were programmed by setting switches and inserting patch leads to
route data and to control signals between various functional units. In the
vast majority of modern computers, the same memory is used for both data
and program instructions. The mechanisms for transferring the data and
instructions between the CPU and memory are, however, considerably more
complex than the original von Neumann architecture.

Harvard architecture
• The Harvard architecture is a computer architecture with physically
separate storage and signal pathways for instructions and data. The
term originated from the Harvard Mark I relay-based computer,
which stored instructions on punched tape (24 bits wide) and data in
electro-mechanical counters. These early machines had limited data
storage, entirely contained within the central processing unit, and
provided no access to the instruction storage as data. Programs
needed to be loaded by an operator, the processor could not boot
itself.
• Today, most processors implement such separate signal pathways
for performance reasons but actually implement a
Modified Harvard architecture, so they can support tasks like
loading a program from disk storage as data and then executing it.

Harvard architecture

Modified Harvard Architecture
• The Modified Harvard Architecture is a
variation of the Harvard computer
architecture that allows the contents of the
instruction memory to be accessed as if it
were data. Most modern computers that
are documented as Harvard Architecture
are, in fact, Modified Harvard Architecture.

Overview of 8085 microprocessor
– 8085 Architecture
1. Cpu of microcomputer
2. 8085 is 8 bit microprocessor
• Pin Diagram
1. 40 pin IC package fabricated on a single LSI
chip.
2. Uses a single +5V DC supply for its use.
• Functional Block Diagram

Intel 8085
• 8 bit NMOS Microprocessor.
• 40 pin IC fabrictaed on single LSI chip
• Uses a single +5v DC supply for its
operation
• Clock speed is 3Mhz.
• Clock cycle is of 320ns
• It has 80 basic instruction and 246
opcodes

Three main sections
• ALU
• A timing and Control unit
• Set of registers

ALU
• Perform the arithmetic operations
1. Addition
2. Subtraction
3. Logical AND
4. Logical OR
5. Logical Exclusive OR
6. Complement (Logical NOT)
7. Increment (add 1)
8. Decrement (Subtract 1)
9. Left Shift ,Rotate Left , Rotate right
10. Clear

Timing and Control unit
• Generates timing and control signals necessary to carry out the
instruction, which has been decoded.
• Control data path (flow) b/w CPU and peripheral (including memory).
• Provide status ,control and timing signals which are requested for the
operation of memory and I/O devices.
• Control entire operations of the microprocessor and peripheral connected
to it.
• CU is the brain of the computer.
• In reality causes certain connections between blocks of the uP to be
opened or closed, so that data goes where it is required, and so that ALU
operations occur.

24
The 8085 Bus Structure
The 8-bit 8085 CPU (or MPU – Micro Processing Unit)
communicates with the other units using a 16-bit address
bus, an 8-bit data bus and a control bus.

25
The 8085 Bus Structure
Address Bus
 Consists of 16 address lines: A0 – A15
 Operates in unidirectional mode: The address
bits are always sent from the MPU to peripheral
devices, not reverse.
 16 address lines are capable of addressing a
total of 216
= 65,536 (64k) memory locations.
 Address locations: 0000 (hex) – FFFF (hex)

26
The 8085 Bus Structure
Data Bus
 Consists of 8 data lines: D0 – D7
 Operates in bidirectional mode: The data bits are
sent from the MPU to peripheral devices, as well
as from the peripheral devices to the MPU.
 Data range: 00 (hex) – FF (hex)
Control Bus
 Consists of various lines carrying the control
signals such as read / write enable, flag bits.

Intel 8085 Registers
• It has following registers, registers are
small due to limited size of the chip:
• One 8-bit ACC (Accumulator).
• 6 Eight bit GPR (B,C,D,E,H and L).
• One 16 bit SP (Stack Pointer)
• One 16 bit PC (Program Counter)
• Instruction Register
• Temporary Register

Set of registers
• Used by the microprocessor for temporary storage and
manipulation of data and instruction.
• Programmer can use these registers to store or copy data into the
registers by using data copy instructions.
• Data remain in register till they are sent to the memory or I/O device.
• one accumulator,
• The 8085 has six general-purpose registers to store 8-bit data;
these are
identified as B,C,D,E,H, and L
• They can be combined as register pairs - BC, DE, and HL - to
perform some 16-bit operations.
• one flag register

• It has two 16-bit registers: the stack
pointer and the program counter.
• Large Computer have more registers so
program requires less transfer of data to/
from the memory.
• Small Computers have less register due to
limited size on chip.

Accumulator (ACC)
• 8 bit register.
• Register A
• Used for storing the operands/data during execution.
• Hold one of the operands of an arithmetic operation.
• Serve as an Input to the ALU.
• The other operand for an arithmetic operation may be stored in the memory or GPR.
• The final result of an operation is placed in the Acc.
• DAD rp for 16 bit addition for which one of the 16 bit operands is kept in H-L and the
other in the B-C or D-E pair. The result is placed in the H-L pair.

Program counter (PC)
• 16 bit special purpose register.
• Used to store the memory address of the next instruction to be executed.
• Keep track of the memory addresses of the instruction in a program while they are
being executed.
• Microprocessor increment the content of PC during the execution of the instruction So
that it points to the adress of the next instruction in the program at the end of the
execution of an instuction.

• Index register – This is used for addressing
index addressing mode.
• Stack pointer – It is a 16 bit register used to
initialize the stack.
• Instruction register – It is a 8 bit register that
stores the instruction fetched from memory

Status register
• The ALU includes five flip-flops, which are set or reset after an operation
according to data conditions of the result in the accumulator and other
registers.
• It stores the present status of the microprocessor after any arithmetic and
logical operation.
• It records any occurrence of carry, auxiliary carry, sign, zero and odd/even
parity.
• The five status flags of Intel 8085 are:
1. Carry Flag (CS)
2. Parity Flag (P)
3. Auxiliary Carry Flag (AC)
4. Zero Flag (Z)
5. Sign Flag (S)

AC (Auxiliary Carry)
• AC hold carry out of the bit number 3 to the bit number 4
resulting from the execution of an arithmetic operation.
• Counting of the bits starts from zero.
• ADD CB and E9
C B = 1100 1011
E 9 = 1110 1001
1011 0100
CY =1
MSB =1 ; S=1
AC =1
Four 1’s ; P=1
Result is non zero ; Z=0

Buses
• It is the interface section for communication between processor and
external devices. There are 3 buses
1. Address bus – It carries the address of the instruction. It is 16 bit
wide and unidirectional.
2. Data bus – It carries data between external devices and processor.
It is 8 bit wide and bidirectional.
3. Control bus – It is used to send control signals to different units of
microprocessor.

8085 Pin description.
Properties
• Single + 5V Supply
• 4 Vectored Interrupts (One is Non Mask able)
• Serial In/Serial Out Port
• Decimal, Binary, and Double Precision Arithmetic
• Direct Addressing Capability to 64K bytes of memory
• The Intel 8085A is a new generation, complete 8 bit
parallel central processing unit (CPU).
• The 8085A uses a multiplexed data bus.
• The address is split between the 8bit address bus and
the 8bit data bus. Figures are at the end of the
document.

Pin Description
The following describes the function of each pin:
• A8 – 16 (Output 3 State): Address Bus; The
most significant 8 bits of the memory address or
the 8 bits of the I/0 address,3 stated during Hold
and Halt modes.
• AD0 - 7 (Input/Output 3state) : Multiplexed
Address/Data Bus; Lower 8 bits of the memory
address (or I/0 address) appear on the bus
during the first clock cycle of a machine state. It
then becomes the data bus during the second
and third clock cycles. 3 stated during Hold and
Halt modes.

• ALE (Output) Address Latch Enable: It occurs during the first clock
cycle of a machine state and enables the address to get latched into
the on chip latch of peripherals.
• The falling edge of ALE is set to guarantee setup and hold times for
the address information.
• ALE can also be used to strobe the status information. ALE is never
3stated.
• SO, S1 (Output)
Data Bus Status. Encoded status of the bus cycle:
1. S1 S0
2. O O HALT
3. 0 1 WRITE
4. 1 0 READ
5. 1 1 FETCH
• S1 can be used as an advanced R/W status.

• RD (Output 3state): READ; indicates the selected
memory or 1/0 device is to be read and that the Data
Bus is available for the data transfer.
• WR (Output 3state):WRITE; indicates the data on the
Data Bus is to be written into the selected memory or 1/0
location. Data is set up at the trailing edge of WR.
3stated during Hold and Halt modes.
• READY (Input): If Ready is high during a read or write
cycle, it indicates that the memory or peripheral is ready
to send or receive data. If Ready is low, the CPU will
wait for
• Ready to go high before completing the read or write
cycle.

• HOLD (Input) :
HOLD; indicates that another Master is requesting the
use of the Address and Data Buses. The CPU, upon
receiving the Hold request. will relinquish the use of
buses as soon as the completion of the current machine
cycle. Internal processing can continue. The processor
can regain the buses only after the Hold is removed.
When the Hold is acknowledged, the Address, Data, RD,
WR, and IO/M lines are 3stated.
• HLDA (Output) :
HOLD ACKNOWLEDGE; indicates that the CPU has
received the Hold request and that it will relinquish the
buses in the next clock cycle. HLDA goes low after the
Hold request is removed. The CPU takes the buses one
half clock cycle after HLDA goes low.

• INTR (Input): INTERRUPT REQUEST; is used as a
general purpose interrupt. It is sampled only during the
next to the last clock cycle of the instruction. If it is
active, the Program Counter (PC) will be inhibited from
incrementing and an INTA will be issued. During this
cycle a RESTART or CALL instruction can be inserted to
jump to the interrupt service routine. The INTR is
enabled and disabled by software. It is disabled by Reset
and immediately after an interrupt is accepted.
• INTA (Output): INTERRUPT ACKNOWLEDGE; is used
instead of (and has the same timing as) RD
• during the Instruction cycle after an INTR is accepted. It
can be used to activate the
• 8259 Interrupt chip or some other interrupt port.
• RST 5.5
• RST 6.5 - (Inputs)
• RST 7.5

RESTART INTERRUPTS:These three inputs have the same
timing as I NTR except they cause an internal RESTART to be
automatically inserted.
RST 7.5 ~~ Highest Priority
RST 6.5
RST 5.5 o Lowest Priority
The priority of these interrupts is ordered as shown above.
These interrupts have a higher priority than the INTR.
•TRAP (Input): Trap interrupt is a non-mask able restart
interrupt. It is recognized at the same time as INTR. It is
unaffected by any mask or Interrupt Enable. It has the highest
priority of any interrupt.

• RESET IN (Input):
Reset sets the Program Counter to zero and resets the
Interrupt Enable and HLDA flipflops. None of the other
flags or registers (except the instruction register) are
affected The CPU is held in the reset condition as long
as Reset is applied.
• RESET OUT (Output):
Indicates CPU is being reset. Can be used as a system
RESET. The signal is synchronized to the processor
clock.
• X1, X2 (Input):
Crystal or R/C network connections to set the internal
clock generator X1 can also be an external clock input
instead of a crystal. The input frequency is divided by 2
to give the internal operating frequency.

• SOD (output): Serial output data line. The
output SOD is set or reset as specified by
the SIM instruction.
• Vcc: +5 volt supply.
• Vss: Ground Reference.

• CLK (Output): Clock Output for use as a
system clock when a crystal or R/ C
network is used as an input to the CPU.
The period of CLK is twice the X1, X2
input period.
• IO/M (Output): IO/M indicates whether the
Read/Write is to memory or l/O Tristated
during Hold and Halt modes.
• SID (Input): Serial input data line The data
on this line is loaded into accumulator bit 7
whenever a RIM instruction is executed.

49
The 8085: CPU Internal Structure
The internal architecture of the 8085 CPU is
capable of performing the following operations:
 Store 8-bit data (Registers, Accumulator)
 Perform arithmetic and logic operations (ALU)
 Test for conditions (IF / THEN)
 Sequence the execution of instructions
 Store temporary data in RAM during execution

50
The 8085: CPU Internal Structure
Simplified block diagram

51
Example: Memory Read Operation

52
Example: Instruction Fetch Operation
 All instructions (program steps) are stored in memory.
 To run a program, the individual instructions must
be read from the memory in sequence, and executed.
 Program counter puts the 16-bit memory address of the
instruction on the address bus
 Control unit sends the Memory Read Enable signal to
access the memory
 The 8-bit instruction stored in memory is placed on the data
bus and transferred to the instruction decoder
 Instruction is decoded and executed

53
Example: Instruction Fetch Operation

54
Example: Instruction Fetch Operation

55
8085 Functional Block Diagram

Addressing modes
• The data are specified in different modes in the
instructions. The various ways of specifying data are
called addressing modes.
• The 8085 microprocessor has 5 types of addressing
modes
1. Immediate Addressing mode
2. Register Addressing mode
3. Direct Addressing mode
4. Indirect Addressing mode
5. Implied Addressing mode

Immediate Addressing mode :
• When the data is directly specified in the
instruction, Which is called immediate
addressing mode.( MVI reg, Data)
Example:
MVI B, 72H
LXI H,5000H

Register Addressing mode
• When the data is stored in the register and
if the register is specified in the instruction,
then it is called register addressing mode .
( MOV Rd., Rs).
• Eg: MOV D, C;
The contents of C is moved to register D.

Direct Addressing mode
• When the memory Address specified with
in the instruction, then it is called direct
addressing mode.
Eg: LDA 5000H;
The 5000H memory content is stored in to
the accumulator.

Indirect Addressing mode
• Load the data , to the accumulator from the
memory. The data which is pointed by the
memory pointer (HL reg),it is called indirect
addressing mode.
• Example:
MOV A, M
The data moved to accumulator from the
memory, which is pointed by the memory
pointer.

Implied Addressing mode
• When the instruction itself specifies the
data to be operated, then it is called
Implied addressing mode.
Example:
CMA - Complement the content of
accumulator.
RRC- rotate accumulator content with out
carry.

Data Transfer Group:
The data transfer instructions move data between registers or between
memory and registers.
• MOV : Move
• MVI : Move Immediate
• LDA :Load Accumulator Directly from Memory
• STA :Store Accumulator Directly in Memory
• LHLD: Load H & L Registers Directly from Memory
• SHLD : Store H & L Registers Directly in Memory
• An 'X' in the name of a data transfer instruction implies that it deals with a
register pair (16-bits);

• LXI : Load Register Pair with Immediate data
• LDAX : Load Accumulator from Address in
Register Pair
• STAX : Store Accumulator in Address in
Register Pair
• XCHG : Exchange H & L with D & E
• XTHL :Exchange Top of Stack with H & L

Arithmetic Group Instructions
• The arithmetic instructions add, subtract, increment, or
decrement data in registers or memory.
• ADD Add to Accumulator
• ADI Add Immediate Data to Accumulator
• ADC Add to Accumulator Using Carry Flag
• ACI Add Immediate data to Accumulator Using
Carry
• SUB Subtract from Accumulator
• SUI Subtract Immediate Data from Accumulator

• SBB Subtract from Accumulator Using Borrow
(Carry) Flag
• SBI Subtract Immediate from Accumulator Using
Borrow (Carry) Flag
• INR Increment Specified Byte by One
• DCR Decrement Specified Byte by One
• INX Increment Register Pair by One
• DCX Decrement Register Pair by One
• DAD Double Register Add; Add Content of
Register Pair to H & L Register Pair

Logical Group
• This group performs logical (Boolean) operations on data in registers
and memory and on condition flags.
• The logical AND, OR, and Exclusive OR instructions enable you to set
specific bits in the accumulator ON or OFF.
• ANA Logical AND with Accumulator
• ANI Logical AND with Accumulator Using Immediate Data
• ORA Logical OR with Accumulator
• OR Logical OR with Accumulator Using Immediate Data
• XRA Exclusive Logical OR with Accumulator
• XRI Exclusive OR Using Immediate Data

• The Compare instructions compare the content of an 8-bit value with the
contents of the accumulator;
• CMP Compare
• CPI Compare Using Immediate Data
• The rotate instructions shift the contents of the accumulator one bit
position to the left or right:
•
• RLC Rotate Accumulator Left
• RRC Rotate Accumulator Right
• RAL Rotate Left Through Carry
• RAR Rotate Right Through Carry
• Complement and carry flag instructions:
•
• CMA Complement Accumulator
• CMC Complement Carry Flag
• STC Set Carry Flag

Branch Group Instructions
• The branching instructions alter normal
sequential program flow, either
unconditionally or conditionally. The
unconditional branching instructions are
as follows:
• JMP Jump
• CALL Call
• RET Return

Conditional branching instructions examine the status
of one of four condition flags to determine whether
the specified branch is to be executed.
The conditions that may be specified are as follows:
• NZ Not Zero (Z = 0)
• Z Zero (Z = 1)
• NC No Carry (C = 0)
• C Carry (C = 1)
• PO Parity Odd (P = 0)
• PE Parity Even (P = 1)
• P Plus (S = 0)
• M Minus (S = 1)
• Thus, the conditional branching instructions are
specified as follows:

Jumps Calls Returns
1. C CC RC (Carry)
2. INC CNC RNC (No Carry)
3. JZ CZ RZ (Zero)
4. JNZ CNZ RNZ (Not Zero)
5. JP CP RP (Plus)
6. JM CM RM (Minus)
7. JPE CPE RPE (Parity Even)
8. JP0 CPO RPO (Parity Odd)

• Two other instructions can affect a branch
by replacing the contents or the program
counter:
• PCHL Move H & L to Program
Counter
• RST Special Restart Instruction
Used with Interrupts

Stack I/O and Machine Control
Instructions
• Stack I/O, and Machine Control Instructions:
• The following instructions affect the Stack
and/or Stack Pointer:
•
• PUSH Push Two bytes of Data onto the
Stack
• POP Pop Two Bytes of Data off the Stack
• XTHL Exchange Top of Stack with H & L
• SPHL Move content of H & L to Stack
Pointer

• The I/0 instructions are as follows:
• IN Initiate Input Operation
• OUT Initiate Output Operation
• The Machine Control instructions are
as follows:
• EI Enable Interrupt System
• DI Disable Interrupt System
• HLT Halt
• NOP No Operation