8085 MICRO PROCESSOR & 8051 MICRO CONTROLLER

    

       ***Draw the pin diagram of 8085 MP and explain each pin

   8085 microprocessor pins are classified into seven groups −

Address bus : A8-A15  It carries higher order 8-bit Address.

Data bus: AD0- AD7  it carries  lower order8- bit Address and data bus.

Control and status signals: These signals are used to identify the nature of operation.

There are 3 control signal and 3 status signals.

Three control signals are RD, WR & ALE.

·      RD − This signal indicates that the selected IO or memory device is to be read and      is ready for accepting data available on the data bus.

·     WR − This signal indicates that the data on the data bus is to be written into a            selected memory or IO location.

·      ALE –Address Latch Enable: When the pulse goes high, it indicates address.          When  the pulse goes down it indicates data.

  Three status signals are IO/M, S0 & S1.

IO/M : This signal is used to differentiate between IO and Memory operations, i.e. when it is high it indicates IO operation and when it is low then it indicates memory operation.

S1 & S0 : These signals are used to identify the type of current operation.

Power supply : There are 2 power supply signals − VCC & VSS. VCC indicates             +5v power supply and VSS indicates ground signal.

Clock signals : There are 3 clock signals, i.e. X1, X2, CLK OUT.

·      X1, X2 − A crystal is connected to these two pins and is used to set frequency of        the internal clock generator. This frequency is internally divided by 2.

·       CLK OUT−This signal is used as the system clock for devices to connect with µp. Interrupts & externally initiated signals

     Interrupts are the signals generated by external devices to request the               microprocessor to perform a task. There are 5 interrupt signals, i.e. TRAP,

  RST 7.5,   RST 6.5, RST 5.5, and INTR.

·         INTA − It is an interrupt acknowledgment signal.

·       RESET IN − This signal is used to reset the µp by setting the program counter to       zero.

·     RESET OUT −This signal is used to reset all the connected devices when the µp is       reset.

·   READY − This signal indicates that the device is ready to send or receive data. If          READY is low, then the CPU has to wait for READY to go high.

·      HOLD −This signal indicates that another master is requesting to use of the                address   and data buses.

·     HLDA (HOLD Acknowledge) − It indicates that the CPU has received the HOLD        request and it will relinquish the bus in the next clock cycle. HLDA is set to low        after the HOLD signal is removed.

Serial I/O signals : There are 2 serial signals, i.e. SID and SOD and these               signals  are used for serial communication.

·        SOD (Serial output data line) − The output SOD is set/reset as specified by the          SIM   instruction.

·       SID (Serial input data line) − The data on this line is loaded into accumulator               whenever a RIM instruction is executed.

***Write a short note on 8085 Interrupts.

Interrupts in 8085

Interrupts are the signals generated by the external devices to request the microprocessor to perform a task. There are 5 interrupt signals, i.e. TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR.

Interrupt are classified into groups based on their parameter −

·         Vector interrupt − In this type of interrupt, each interrupt contains particular address.  For example: RST7.5 (003CH), RST6.5 (0034H), RST5.5 (002CH),TRAP (0024H).

·         Non-Vector interrupt − In this type of interrupt, the interrupt address is not known to the processor so, the interrupt address needs to be sent externally by the device to perform interrupts. For example: INTR.

·         Maskable interrupt − In this type of interrupt, we can disable the interrupt by writing DI instruction and we can enable the instruction by EI instruction.(OR) by writing some instructions into the program. For example: RST7.5, RST6.5, RST5.5.

·         Non-Maskable interrupt − In this type of interrupt, we cannot disable the interrupt by writing some instructions into the program. For example: TRAP.

·         Software interrupt − In this type of interrupt, the programmer has to add the instructions into the program to execute the interrupt. There are 8 software interrupts in 8085, i.e. RST0, RST1, RST2, RST3, RST4, RST5, RST6, and RST7.

·         Hardware interrupt − There are 5 interrupt pins in 8085 used as hardware interrupts, i.e. TRAP, RST7.5, RST6.5, RST5.5, INTA.

Note − NTA is not an interrupt, it is used by the microprocessor for sending acknowledgement. TRAP has the highest priority, then RST7.5 and so on.

*** Explain 8085 Architecture (OR) Functional Blocks (OR) Register Organization.

8085 is an 8-bit microprocessor designed by Intel in 1977 using NMOS technology.

Features of 8085:

·         8-bit data bus

·         16-bit address bus, which can address upto 64KB

·         A 16-bit program counter

·         A 16-bit stack pointer

·         Six 8-bit registers arranged in pairs: BC, DE, HL

·         Requires +5V supply to operate at 3.125 MHZ single phase clock

It is used in washing machines, microwave ovens, mobile phones, etc.

8085 Microprocessor – Functional Units :

Accumulator

It is an 8-bit register used to perform any arithmetic, logical, I/O operation one of the operand must be stored in it and after completing the operation result will automatically stored in Accumulator. It is connected to internal data bus & ALU.

Arithmetic and logic unit

It performs arithmetic and logical operations like Addition, Subtraction one bit increment ,decrement, AND, OR, Compare, rotate etc. on 8-bit data.

General purpose register

There are 6 general purpose registers in 8085 processor, i.e. B, C, D, E, H & L. Each register can hold 8-bit data.

These registers can also use as 16-bit pairs to hold 16-bit data. The pairs are B-C, D-E & H-L.

Program counter

It is a 16-bit register used to store the memory address location of the next instruction to be executed. Microprocessor increments the program whenever an instruction is being executed, so that the program counter increment the memory address of the next instruction that is going to be executed.

Stack pointer

It is also a 16-bit register works like stack, which is always incremented/decremented by 2 during push & pop operations.

Temporary register

It is an 8-bit register, which holds the temporary data of arithmetic and logical operations.

Flag register

It is an 8-bit register having five 1-bit flip-flops, which holds either 0 or 1 depending upon the result stored in the accumulator.

These are the set of 5 flip-flops −

·         Sign (S)

·         Zero (Z)

·         Auxiliary Carry (AC)

·         Parity (P)

·         Carry (C)

Its bit position is shown in the following table −

D7	D6	D5	D4	D3	D2	D1	D0
S	Z		AC		P		CY

Instruction register and decoder

It is an 8-bit register. When an instruction is fetched from memory then it is stored in the Instruction register. Instruction decoder decodes the information present in the Instruction register.

Timing and control unit

It provides timing and control signal to the microprocessor to perform

·         Control Signals: READY, RD’, WR’, ALE

·         Status Signals: S0, S1, IO/M’

·         DMA Signals: HOLD, HLDA

·         RESET Signals: RESET IN, RESET OUT

Interrupt control

It controls the interrupts during a process. When a microprocessor is executing a main program and whenever an interrupt occurs, the microprocessor shifts the control from the main program to process the incoming request. After the request is completed, the control goes back to the main program.

There are 5 interrupt signals in 8085 microprocessor: INTR, RST 7.5, RST 6.5, RST 5.5, TRAP.

Serial Input/output control

It controls the serial data communication by using these two instructions: SID (Serial input data) and SOD (Serial output data).

 Address buffer and address-data buffer

The content stored in the stack pointer and program counter is loaded into the address buffer and address-data buffer to communicate with the CPU. The memory and I/O chips are connected to these buses; the CPU can exchange the desired data with the memory and I/O chips.

Address bus and data bus

Data bus carries the data to be stored. It is bidirectional, whereas address bus carries the location to where it should be stored and it is unidirectional. It is used to transfer the data & Address I/O devices.

*** Explain the 8085 Instruction set

The 8085 Instruction Classification can be categorized into five different groups based on the nature of function of the instructions

·         Data transfer operations

·         Arithmetic operations.

·         Logical operations

·         Branch operations

·         Stack, Input/Output and Machine control operations

1.Data Transfer Operations: Data transfer instructions copy data from source to destination. Source can be data or contents of register or contents of memory location whereas destination can be register or memory location. These instructions do not affect the flag register of the processor.

2..Arithmetic Operations 8085 perform addition, subtraction, increment and decrement operations.

Addition : Any 8-bit number, or the contents of a register, or the contents of a memory location can be added to the contents of the accumulator and the resulted sum is stored in the accumulator. The resulted carry bit is stored in the carry flag.

In 8085, no two other registers can be added directly, i.e. the contents of B and C registers cannot be added directly. To add two 16-bit numbers the 8085 provides DAD instruction. It adds the data within the register pair to the contents of the HL register pair and resulted sum is stored in the HL register pair.

Subtraction : Any 8-bit number, or the contents of a register, or the contents of a memory location can be subtracted from the contents of the accumulator and the result is stored in the accumulator. The resulted borrow bit is stored in the carry flag: In 8085, no two other registers can be added directly.

Increment/Decrement : The 8085 has the increment and decrement instructions to increment and decrement the contents of any register, memory location or register pair by 1.

3.Logical Operations: The logical instructions provided by 8085 perform logical, rotate, compare and complement operations.

Logical : Using logical instructions, any 8-bit number, or the contents of a register, or of a memory location can be logically ANDed, ORed, or Exclusive-ORed with the contents of the accumulator and the result is stored in the accumulator. The result also affects the flags according to definition of For example, the zero result sets the zero flag.

Rotate : These instructions allow shifting of each bit in the accumulator either left or right by 1 bit position.

Compare : Any 8-bit number, or the contents of a register, or the contents of a memory location can be compared for equality, greater than, or less than, with the contents of the accumulator.

Complement : The result of accumulator can be complemented with this It replaces all 0s by 1s and all 1s by 0s.

4.Branching Operations: These instructions allow the 8085 to change the sequence of the program, either unconditionally or under certain test conditions. These instructions include branch instructions, subroutine call and return instructions and restart instructions.

5.Stack, Input/Output and Machine Control Operations: These instructions control the stack operations, input/output operations and machine operations. The stack instructions allow the transfer of data from register pair to stack memory and from stack memory to the register, pair. The input/output instruction allows the transfer of 8-bit data to input/output port. On the other hand machine instructions control the Machine operations such as interrupt, halt, or do nothing.

*** Explain the Bus organization of 8085 µp. (OR) Write a short note on system bus

Bus is a group of conducting wires which carries information, all the peripherals are connected to microprocessor through Bus.

There are three types of buses.

1.Address Bus

2.Data Bus

3.Control Bus

1.Address Bus:-8085 Microprocessor has 16 bit address bus. The address bus carries the address of memory location to be written or to be read from.

The address bus is unidirectional, that means bits flowing only in one direction, only from microprocessor to peripheral devices.

We can find that how much memory location it can using the formula 2^N. where N is the number of bits used for address lines.

In 8085 µp:    2¹⁶ = 65,536bytes or 64Kb

So we can say that it can access upto 64 kb memory location.

2.Data Bus:-8085 Microprocessor has 8 bit data bus. So it can be used to carry the 8-bit data starting from 00000000H(00H) to 11111111H(FFH). Here 'H' tells the Hexadecimal Number. It is bidirectional. These lines are used for data flowing in both direction means data can be transferred or can be received through these lines.

The data bus also connects the I/O ports and CPU. The largest number that can appear on the data bus is 11111111.

It has 8 parallel lines of data bus. So it can access upto 2⁸ = 256 data bus lines.

3.Control Bus:-The control bus is used for sending control signals to the memory and I/O devices. The CPU sends control signal on the control bus to enable the outputs of addressed memory devices or I/O port devices.

Some of the control bus signals are:

1.Memory read

2.Memory write

3.I/O read

4.I/O write.

Unit-3

Explain the overview of 8051 Micro controller.

1. 8051 microcontroller is designed by Intel in 1981. It is an 8-bit microcontroller.

2. It is built with 40 pins DIP (dual inline package), 4kb of ROM storage and 128 bytes of RAM storage. 2 16-bit timers.

3. It consists of four parallel 8-bit ports ( which are programmable as well as addressable as per the requirement). Its crystal frequency is 12 MHz.

4.The system bus connects all the support devices to the CPU. The system bus consists of an 8-bit data bus, a 16-bit address bus and bus control signals.

5.All other devices like program memory, ports, data memory, serial interface, interrupt control, timers, and the CPU are all interfaced together through the system bus.

Draw the pin Diagram of 8051 Microcontroller and explain each pin

The pin diagram of 8051 microcontroller –

Pins 1 to 8 − These pins are known as Port 1. This port doesn’t serve any other functions. It is internally pulled up, bi-directional I/O port.

·      Pin 9 − It is a RESET pin, it is used to reset the microcontroller to its initial values.

·    Pins 10 to 17 − These pins are known as Port 3. This port serves some functions like interrupts, timer input, control signals, serial communication signals RxD and TxD, etc.

·      Pins 18 & 19 −These pins are used to get the system clock.

·       Pin 20 & 40 − This pin is connected to GND. Pin 40 is connected to power supply.

·      Pins 21 to 28 − These pins are known as Port 2. It serves as I/O port. Higher order address bus signals are also multiplexed  on this port.

·     Pin 29 − This is PSEN (Program Store Enable). It is used to read a signal from the external program memory.

·    Pin 30 − This is EA pin which stands for External Access input. It is used to enable/disable the external memory interfacing.

·    Pin 31 − This is ALE pin which stands for Address Latch Enable. It is used to demultiplex the address-data signal of port.

·        Pins 32 to 39 − These pins are known as Port 0. It serves as I/O port. Lower order address and data bus signals are multiplexed using this port.

·         Pin 40 − This pin is used to provide power supply to the circuit