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 set up and hold times for the address information. ALE can also be used to store the status information.

RD(Output3state):

• READ: indicates the selected memory or I/0 device is to be read and that the Data Bus is available for the data transfer.

WR (Output3state):

• WRITE: indicates the data on the Data Bus is to be written into the selected memory or I/0 location. Data is set up at the trailing edge of WR. 3stated during Hold and Halt modes.

IO/M,S0,S1:

• IO/M indicates whether input output operation or memory operation is being carried out.
• S0 and S1 indicated the type os machine cycle in progress.

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.

Size of data bus =8 bits

Size of address bus=16bit

Size of memory word=8 bit

Memory capacity=64kb

This is used to demultiplex AD0 to AD7 lines to A0-A7 and D0-D7.

The separation of address line and data line is achieved by connecting a external latch to AD0-AD7 lines and enabling the latch when ALE signal is active.

• Logic output has two states LOW and HIGH corresponding to the logic value 0 and 1.

• However some output have a third electrical state that is not logical called high impedance or floating state.

• In this state the output behaves as if it is not even connected to circuit except small leakage current that may flow into or out of the output pin. This state is tristate logic

 The five interrupt pins available in 8085 are

·        TRAP

·        RST 7.5

·        RST 6.5

·        RST 5.5

·        INTR

• The stack is a reserved area of memory in the RAM where temporary information may be stored.

• A 16 bit stack pointer is used to hold the address of most recent stack entry.

Parity Flag (PF): This flag is used to indicate the parity of result. If lower order 8-bits of the result contains even number of 1‟s, the Parity Flag is set and for odd number of1‟s,the Parity Flag is reset.

Zero Flag(ZF) :It is set; if the result of arithmetic or logical operation is zero else it is reset.

The important signal in 8085 microprocessor are: ALE,IO/M,RD/WR.

Generally I/O devices are slow devices. Therefore the speed of I/O devices does not match with the speed of microprocessor. And so an interface is provided between system bus and I/O devices.

The address is an identification number used by the microprocessor to identify or access a memory location or I / O device. It is an output signal from the processor. Hence the address bus is unidirectional.

The software developed using 1's and 0's are called machine language, programs. The software developed using mnemonics are called assembly language programs.

The basic units or blocks of a microprocessor are ALU, an array of registers and control unit

Instruction cycle is defined as the time required completing the execution of an instruction.

Machine cycle is defined as the time required completing one operation of accessing memory, I/O or acknowledging an external request.

T –cycle is defined as one subdivision of the operation performed in one clock period.

The 8085 have seven machine cycles they are

• Opcode fetch
• Memory read
• Memory write
• I/O read
• I/O write
• Interrupt acknowledge

An instruction is a binary pattern entered through an input device to command the microprocessor to perform that specific function.

There are 74 operations in the 8085 microprocessor

• Data transfer group–MOV,MVI,LXI

• Arithmetic group–ADD,SUB,INR.

• Logical group-ANA,XRA,CMP.

• Branch group–JMP,JNZ,CALL.

• StackI/O and machine control group–PUSH,POP,IN,HLT.

JMP instruction permanently changes the program counter. A CALL instruction leaves Information on the stacks that the original program execution sequence can be resumed.

The IN instruction is used to move data from an I/O port into the accumulator.

The OUT instruction is used to move data from the accumulator to an I/Oport.

The IN and OUT instructions are used only on microprocessor, which usea separate address space for interfacing.

A rotate instruction is a closed loop instruction. that is the data moved out at one end is put back in at the other end. The shift instruction loses the data that is moved out of the last bit locations.

• DI(disable interrupts)

• EI(enable interrupts)

• RIM(read interrupt masks)

• SIM(set interrupt masks)

The instructions of 8085 can be categorized into the following five

1. EI

2. DI

3. NOP

4. HLT

5. SIM

6. RIM

LDA copies the data byte into the accumulator from the memory location specified by the 16-bit address.STA copies the data byte from the accumulator in the memory location specified by 16-bitaddress. DAA changes the content of the accumulator from binary to 4-bit BCD digits

The instruction set is grouped into the following formats One by the instruction MOV C,A Two byte instruction MVI A,39H Three byte instruction JMP2345H

The various formats of specifying the operands are called as addressing modes, it is used to access the operands or data. The different types are as follows

1. Immediate addressing

2. Register addressing

3. Direct addressing

4. Indirect addressing

5. Implicit addressing

The stack is a group of memory locations in the R/W memory that is used for the temporary storage of binary information during the execution of the program. The stack related instructions are PUSH and POP

The XRAA instruction is used to clear the contents of the accumulator and store the value 00H

• Procedures are group of instructions stored as a separate program in memory and it is called from the main program in memory and it is called from the main program when ever required.

• The type of procedure depends on where the procedures are stored in memory. If it is in the same code segment as that of the main program then it is an ear procedure other wise it is a far procedure.

A device that contains a microprocessor with integrated peripherals like memory, serial ports, parallel ports, timer/counter, interrupt controller, and data acquisition interfaces like ADC, and DAC is called a microcontroller.

DJNZ Rn decrement the content of the register Rn and jump if not zero.

DJNZ direct, rel Decrement the content of direct8 –bit address and jump if not zero

·       RS1,RS0-Register bank select bits

·       RS1,RS0-Bank

·       Bank0

·       Bank1

·       Bank2

·       Bank3

·       RDWRT1T0

·       INT1INT0TXDRXD

·       RD–Read data control output

·       WR–Write data control output

·       T1– Timer/counter1 external input or test pin T0– Timer/counter0 external input or test                 pin INT1–Interrupt1 input pin

·       INT0– interrupt0 input pin

·       TXD–Transmit data pin for serial port in UART mode

·       RXD–Receive data pin for serial port in UART mode

Single instruction, which clears the most significant bit of Bregister of 8051,without affecting the remaining bits, is CLRB.7.

·        Calculators

·        Traffic light control system

·        Game machine

·        Military applications.

The 8051 can access upto 64 kilobyte of program memory and 64 kilo byte of data memory.

• Accumulator
• B Register
• Program status Word.
• Stack pointer.
• Data pointer
• Port 0
• Port 1
• Port 2
• Port 3
• Interrupt priority control register. Interrupt enable control register.

ü  EAET2ES

ü  ET1EX1ET0EX0

ü  EA-Enableallcontrolbit.

ü  ET2-Timer2 interruptenablebit.

ü  ES- Enableserialport controlbit.

ü  ET1-EnableTimer1controlbit.

ü  EX1-Enableexternalinterrupt1controlbit.

ü  ET0-EnableTimer0controlbit.

ü  EX0-Enableexternalinterrupt0controlbit.

ü The interrupt are: Vector address

ü External interrupt0:IE0:0003H

ü Timers interrupt0: TF0:000BH

ü External interrupt1:IE1:0013

ü T imersinterrupt1:TF1:001BH

ü Serial interrupt

ü Receiveinterrupt:RI:0023H Transmitinterrupt:TI:0023H

The features are

ü  Single supply +5 volt operation using HMOS technology.

ü  4096 bytes program memory on chip (not on 8031)

ü  128 data register banks

ü  Four register mode,16-bit timer/counter.

ü  Extensive Boolean processing capabilities.

ü  64 KB external RAM size

ü  32 bi-directional individually addressable I/O lines.

ü  8 bit CPU optimized for control applications.

·        Direct addressing

·        Register addressing

·        Register in direct addressing Implicit addressing Immediate addressing

·        Index addressing

·        Bit addressing

Each of the three counters of 8253 can be operated in one of the following six modes of operation.

1. Mode 0 (Interrupt on terminal count) 2. Mode 1 (Programmable monoshot)

3. Mode 2 (Rate generator) 4. Mode 3 (Square wave generator)

·        This chip converts the parallel data in to a serial stream of bits suitable for serial transmission. It is also able to receive a serial stream of bits and converts it in to parallel data bytes to be read by a microprocessor.

ü  Synchronous data transfer

ü  Asynchronous data transfer

ü  Interrupt driven data transfer

It is a data method which is used when the I/O device and the microprocessor match in speed. The transfer a data to or from the device ,the user program issues a suitable instruction addressing the device. The data transfer is completed at the end of the execution of this instruction.

Two groups A and group B are available for stored Data transfer.

Each group contains one 8-bit data I/O port an done4-bit control/data port.

The8-bit data port can be either used as input or output port. The inputs and outputs both are latched.

Each of the three counters of 8253 can be operated in one of the following six modes of operation.

ü  Mode0 (Interrupt on terminal count)

ü  Mode1 (Programmable mono shot)

ü  Mode2 (Rate generator)

ü  Mode3 (Square wave generator)

ü  Mode4 (Software triggered strobe)

ü  Mode5 (Hardware triggered strobe)

The command words of 8259A are classified in two groups

ü  Initialization command words(ICWs)

ü  Operation command words(OCWs)

ü  The scan counter has two modes to scan the key matrix and refresh the display. In the encoded mode ,the counter provides binary count that is to be externally decoded to provide the scan lines for keyboard and display

ü  .In the decoded scan mode, the counter internally decodes the least significant 2bit and provides a decoded1 out of 4scan on SL3-SL3.The keyboard and display both are in the same mode at a time.

• Scanned Keyboard mode with 2Key Lockout
• Scanned keyboard with N-Key Rollover.
• Scanned Keyboard Special Error Mode.
• Scanned Matrix Mode.

The modem control unit handles the modem handshake signals to coordinate the communication between them on demand the USART.

ü  Mode0-Simple Input/Output.

ü  Mode1-Strobe Input/Output (handshake mode)

ü  Mode2-Strobe bi-directional mode.

It is a word stored in a register (control register) used to control the operation of a program digital device.

The control words written to control register specify an I/O function for each I/O port. The bit D7of the control word determines either the I/O functions of the BSR function.

ü  Port-A:8-bits

ü  Port-B:8-bits

ü  Port-CU :4-bits

ü  Port-CL:4-bits

USART stands for universal Synchronous/Asynchronous Receiver/Transmitter.It is a programmable communication interface that can communicate by using either synchronous or asynchronous serial data.

MOV DPL,#55H

MOV A,DPLRL A

LABEL :SJMP Label

MOV A,#3CH

MOVR4,#66H

ANLA,R4

A3C R466

A24

In this mode serial enters & exits through RXD ,TXD output the shift clock8 bits are transmitted or received 8 data bits(LSB first).the baud rate is fixed at 1/12 the oscillator frequency.

In this mode 11bits are transmitted (through TXD)or received(through RXD)A start bit(0), 8 data bits(LSB first),a programmable 9thdata bit & a stop bit(1) ON transmit the 9thdata bit (TB*in SCON) can be assigned the value of 0or1.or fo reg :the parity bit (p,in the PSW)could be movedintoTB8.

A microprocessor is a processing unit of electronic devices which is including multiple transistors, diodes, register, etc electronics components. The microprocessor can operate arithmetic and logical operations as well as connect with other electronic devices for communication.

The Microprocessor made up of three terms:

• ALU(Arithmetic Logical Unit): This is used for arithmetic and logical performance which is received by memory or input data.
• Register Array: this is used for access and store the data in memory location temporarily using instruction and make the operation successful. Register array consists of Accumulator and B, C, D, E, H, L registers.
• Control Unit: Control Unit controls the data and instruction flow in the system.

The basic diagram of the microprocessor is below.

The 8085 (eight zero eight five) microprocessor is an 8-bit microprocessor. It is developed by Intel using NMOS technology and introduced in 1976, March. The 8085 is the version of 8080 microprocessor were added to the interrupt and serial input/output features.

The 8085 microprocessor has an 8-bit data width and 16-bit address width. This microprocessor has 60 pins. This is used for many electronic devices like oven, mobiles, etc.

The interrupt in the microprocessor is a signal which is generated by external peripherals. The external peripherals (device) send the request to the microprocessor to execute their performance and stop the current task.

After working on the external task, the microprocessor completes the previous task again.

There are five interrupt in the microprocessor which is:- RST 5.5, 6.5, 7.5, INTR, TRAP.

The 8086 microprocessor is a 16-bit microprocessor. It is a developer by Intel and it is an advanced version of 8085.

This processor has a 16-bit data width, a 20-bit address width, and 1MB memory storage.

It provides a powerful instruction set. Using 8086 microprocessor make some operation like multiplication and division and so on easily.

The Bus is common terms in the microprocessor which is mostly used for transmission. The system of the bus is to transmit the data/information and address in binary form.

The bus is a collection of wires that means one wire per binary bit. In microprocessor have three types of the bus which is following.

1. Address Bus: This is the unidirectional bus which is transmitting the address in binary form. The bus transmits data from the microprocessor to memory or input/output devices.
2. Data Bus: The data bus is bidirectional and carries the data and information. This data flow both direction which means from memory/devices to microprocessor and from microprocessor to memory or input/output devices

Control Bus: This is used to control the signal and other peripherals to flow data and transfer to the required memory location

The Flag register is a Special Purpose Register which shows the status of the task. This is an 8-bit register but the only 5bit is used for the operation. The flag becomes set or reset after arithmetic and logical operation.

The flag register has 5 flags which are Sign flag, Zero flag, Auxiliary carry flag, Parity flag, and the Carry flag.

The microprocessor connects with many internal and external devices to process the task successfully. This procedure called interfacing in a microprocessor. In the microprocessor has i/o interfacing and memory interfacing. The connectivity of input devices (keyboard) and output devices (screen) with a microprocessor called I/O interfacing. The microprocessor accesses the memory to read the instruction code and store the data called memory interface.

The register in the microprocessor is a temporary storage location in CPU. The register stores the data and addresses temporary for operation.

The stack is data structure in the RAM area which is worked last in first out. It is used for operation between two registers like swap, add, etc

The polling method used for checking, the state of preparedness of external devices connection.

Interface refers to the path for communication between two components. Interfacing is of two types, memory interfacing, and I/O interfacing.

Memory Interfacing occurs when we need the microprocessor to access the memory for reading instruction codes and the data stored in the memory.

IO Interfacing indicates the various communication devices like the keyboard, mouse, printer, etc. When we need to interface the keyboard and other devices with the microprocessor by using latches and buffers. This type of interfacing is known as I/O interfacing.

The subroutine in the microprocessor is a sequence of program instructions code that performs a particular task. This is packaged as a unit and used in a particular task when needed.

A subroutine is a unit which is used in multiple times in different location. The four types of subroutine have in the microprocessor.

1. Conditional Call instruction,
2. Unconditional call instruction,
3. Conditional return instruction,
4. Unconditional return instruction.

The pipelining is an advance microprocessor technique or procedure. This is worked when the second task work before the first task. This technique used simultaneously at many processing task stages. This is helped to improve task performance. There have 5 stages of working; Instruction Fetch, Instruction Decode, Instruction Execute, Memory Access, write back Instruction.

The Opcode is operation codes in the microprocessor which is done addition, multiplication, etc operation.

The operand contains the data or memory location in the register. If operation worked 1+2 then 1 and 2 are operands.

The macro in the microprocessor is a set of instruction which is group into a single unit. The macro works less than ten instruction set.

The 16-bit microprocessor has a 16-bit data width, 20-bit address width, and 1MB memory storage. This has a powerful instruction set to do many operations. 8086 is an example of a 16-bit microprocessor.          

The 8-bit microprocessor has an 8-bit data width, a 16-bit address width. The 8085 is an example of an 8-bit microprocessor.

The assembler in microprocessor used to convert instruction code to machine code. The instruction code is understood for human and machine code is binary code which is understood to machine code.

The data bus is bidirectional and carries the data and information. This data flow both direction which means from memory/devices to microprocessor and from microprocessor to memory or input/output devices. The data bus either 8bit or 16 bit.

The memory mapping is used to transfer the logical address space into physical memory but sometimes physical memory is a smaller size. The microprocessor can access external memory. The memory mapping used for increased access to physical memory.

The mnemonic in the microprocessor is acronym/abbreviation, for operation. It is used mnemonics in instruction code to make easy and suitable coding. The mnemonics are R used for the register, A for the accumulator, z for zero flags, add for addition, etc.

An embedded microprocessor is a computer microchip used inside many devices and electronics types of equipment. It is provides added functionality like operations and communication with the internet and other devices. It is an integrated circuit working with low power in electrical and electronic appliances as well as real-time data devices.

The analog signal converted into a digital signal helping by the ADC in the microcontroller. It is an 8-bit chip which has eight-channel for conversion. Analog data has binary converted into digital using logical operation.

The ALE is an acronym of Address Enable Latch. If pulse goes high i.e. ALE=1, it means address bus enable and pulse goes low i.e. ALE=0, it means data bus enable. The ALE controls the signal when the pulse goes high because the new task started.

If data want to move one place to another place then data stored temporarily in the buffer. The address and data buffer has bidirectional data transfer. If the buffer has the least significant address then it worked unidirectional data buffer. Without loose data, the buffer can transfer data from electronic devices to microprocessors and vice versa.

The rate of completing the process cycle in the microprocessor called clock speed. The clock speed measured by megahertz or gigahertz unit. 1.8 GHz processor has double clock speed than the 900MHZ processor.

Loaders load the all code into memory and execute the process or Task. Loader calculates the instruction and data size and makes space for memory. It initializes the many registers to execute.

The 8086 has a 16-bit microprocessor which is 40 pins available. 16 data bus, 20 address bus, 2 ground pin, 1 reset pin, and 1 supply pin.

The first microprocessor is invented in1971. It is 4 bit Intel 4004 microprocessor.

If a task needs to take immediate input from the user then MVI instruction is used. This MVI needs 2 Machine cycles for the execution. The syntax of mvi is below.

MVI register_name, value. The value is in hexadecimal.

Example,MVI A 24H.

The microprocessor called also logic chips. The microprocessor does arithmetics and logical operation. The AND, OR, NOT, EXOR, has their instruction in the microcontroller. The logical operations are done by a microprocessor using a register and bus.

Difference between microprocessor and microcontroller

The microprocessor - used in the computer system. Memory and I/O device connected externally. The microprocessor actually processes the data.

The microcontroller - used in the embedded system. The memory and I/O devices have inbuilt. The microcontroller determines the process of data.

The program counter stores the address of the next instruction to be fetched. Thus it is used as a pointer to the instruction.