Microprocessors and Interfacing

Processor

• It is a device that perform an operation on data based on some pre-defined instructions for example Addition

• In starting the CPU were made on different boards and connected together, as technology improved, it became possible to bring whole CPU on a single chip named as microprocessor.

MicroprocessorA Microprocessor is a multipurpose, programmable electronic device that reads binary instruction from memory; accepts binary data as Input and provides output after processing the data.

Block Diagram of computer with Microprocessor as CPU (Microcomputer)

Block Diagram of computer

Brain

• It gets input from eyes/ears and sends processed information to output devices such as face/Muscles.

• Example : Sit down as instruction.

Microprocessor (MPU)

– Read instructions– Process binary data– Microprocessor includes

ALU, Register arrays and control unit on a single chip

Input/Output Devices & Bus

• Input Devices– Keyboard and Switches– Provide binary information to the MPU

• Output devices– LEDs and LCDs– Receive binary information from the MPU

• Bus – Carries bits between the microprocessor and memory and I/O Devices

Microprocessor-Based System with Bus Architecture

Microcontroller

• A device that includes microprocessor, memory and I/O signal lines on a single chip.

Difference between Microcontroller and Microprocessor

10

Microprocessor • CPU is stand-alone, RAM,

ROM, I/O, timer are separate• designer can decide on the

amount of ROM, RAM and I/O ports.

• versatility, general-purpose• High power consumption

Microcontroller• CPU, RAM, ROM, I/O and

timer are all on a single chip• fixed amount of on-chip ROM,

RAM, I/O ports• specific-purpose (control-

oriented)• Low power consumption

Microprocessor Evolution andTypes

Advances in Semiconductor Technology

• SSI <10 Gates• MSI Between 10 to 1000 Gates• LSI >1000 Gates• VLSI >100000

Intel Microprocessors 4,8,16,32,64 Bit Processors

Processor Year of Introduction

Address Bus ( In Bits)

Data Bus( In Bits)

Addressable Memory

4004 1971 10 4 640 Bytes

8080 1974 16 8 64 K Bytes

8085 1976 16 8 64 K Bytes

8086 1978 20 16 1 M Bytes

80386 1985 32 32 4 G Bytes

Pentium II onwards

1997 36 64 64 G Bytes

8085 Hardware Model

ALU• The ALU performs the following arithmetic and logical

operations.– Addition– Subtraction– Logical AND– Logical OR– Logical EXCLUSIVE OR– Complement (logical NOT)– Increment (add 1)– Decrement (subtract 1)– Left shift– Clear

Instruction Register and Decoder

• The instruction register and the decoder are considered as a part of the ALU

• The instruction register is a temporary storage for the current instruction of a program

• The decoder decodes the instruction and establishes the sequence of events to follow

8085 Programming Model

General Registers• 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• The programmer can use these registers to store or copy

data into the registers by using data copy instructions• The HL register pair is also used to address memory

locations• In other words, HL register pair plays the role of memory

address register

Accumulator

• Hold data for manipulation (arithmetic, logical).• Whenever the operation combines two words, either

arithmetically or logically, the accumulator contains one word (say A) and the other word(say B) may be contained in a register or in memory location. After the operation the result is placed in the Accumulator replacing the word A.

• Major working register. • Microprocessor can directly work on Acc.

Program counter

• The function of the PC is to point to the memory address from which the next byte is to be fetched.

• For 8085 it is 16 bit long.• PC automatically increments to point to the next

memory during the execution of the present instruction.

• PC value can be changed by some instructions.

Stack pointer

• 16 bit register acts as memory pointer.• Can save the value of the program counter for

later use.• points to a memory location in R/W memory

which is called stack. follows LIFO algorithm.• After every stack operation SP points to next

available location of the stack. Usually decrements.

Flags

• 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

• They are called Zero (Z), Carry (CY), Sign (S), Parity (P), and Auxiliary Carry (AC) flags

Flag register

S Z AC P CY 1. S : after the execution of an arithmetic operation, if bit 7 of the result is 1, then sign flag is set.

2. Z : bit is set if ALU operation results a zero in the Acc or registers.

3. AC: bit is set, when a carry is generated by bit 3 and passed on bit 4.

4. P: parity bit is set when the result has even number of 1s.For odd no of 1’s , the flag is reset

5. CY = carry is set when result generates a carry. Also a borrow flag.

The 8085 Instruction Set

Data Transfer (Copy) Operations

Types Examples

1. Between Registers 1. MOV B,D – Copy the contents of the register D into Register B

2. Specific data byte to a register or a memory location

2. MVI B,32H – Load register B with the data byte 32H

3. Between a memory location and a register

3. LXI H, 2000H

MOV B,M

From a memory location 2000H to register B

4. Between an I/O device and the accumulator

4. IN 05H – The contents of the input port designated in the operand are read and loaded into the accumulator

Arithmetic Operations

• ADD B – [A] <----- [A]+[B]• ADD M - [A] <----- [A]+[[HL]]• SUB C – [A] <----- [A]-[C]• SUI 76H – [A] <---- [A]-76H

Logical Operations

• ANA B – [A] <----- [A] AND [B]• ANI 85H – [A] <----- [A] AND 85H• ORA M – [A] <----- [A] OR [[HL]]• XRA B – [A] <------ [A] XOR [B]

• Rotate• Compare• Complement

Branching Operations

• JMP 2050H – [PC] <----- 2050H• JZ 3100H – [PC] <----- 3100H if Z=1,

otherwise [PC] <----- [PC]+1• JNC 4250H – [PC] <----- 4250H if

C=0, otherwise [PC] <----- [PC]+1

• Call, Return

Machine Control Operations

• Halt• Interrupt

Instruction Word Size

• In terms of bytes:

• One Byte Instructions• Two Byte Instructions• Three Byte Instruction

One Byte Instructions

Two Byte Instructions

Three Byte Instruction

• JMP 2085H• LDA 2050H

Writing Assembly Language Program

• Define the problem clearly and make the problem statement.

• Analyze the problem thoroughly. In this step we divide the problem into smaller steps to examine the process of writing programs.

• Draw the flow chart. The steps listed in the problem analysis and the sequences are represented in a block diagram.

• Translate the blocks shown in the flowchart into 8085 operations and then subsequently into mnemonics.

Conversion and Execution

• Convert the mnemonics into Hex code; we need to look up the code in 8085 instruction set.

• Store the program in Read/Write memory of a single-board microcomputer. This may require the knowledge about memory addresses and the output port addresses.

• Finally execute the program.