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 smallestaddressable unit are stored in memory the question arises,

“Is the least significant part of the word stored at thelowest address (little Endian, little end first) or–

is the most significant part of the word stored at thelowest address (big Endian, big end first)”?

Example: The hexadecimal 16-bit number ABCDH, stored at address 0:

AB CDmsb ... lsb

ABCD0

1

ABCD

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 microcomputer2. 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 operations1. Addition2. Subtraction3. Logical AND4. Logical OR5. Logical Exclusive OR6. 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.

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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.

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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)

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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 1011E 9 = 1110 1001

1011 0100CY =1 MSB =1 ; S=1AC =1 Four 1’s ; P=1Result 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 S02. O O HALT3. 0 1 WRITE4. 1 0 READ5. 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 PriorityRST 6.5RST 5.5 o Lowest PriorityThe 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.

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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

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The 8085: CPU Internal Structure

Simplified block diagram

51

Example: Memory Read Operation

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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

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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 modes1. Immediate Addressing mode2. Register Addressing mode3. Direct Addressing mode4. Indirect Addressing mode5. 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, MThe 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