Microprocessor, Memory & IO

8/3/2019 Microprocessor, Memory & IO

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MICROPROCESSOR,MICROPROCESSOR,MEMORY & I/OMEMORY & I/O


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Generalized Microprocessor

What the P does? Reads one instruction at a time from memory

Performs data manipulation

ea s ata rom nput ev ces an wr tes ata tooutput devices

When the P is executing a program, it

communicates frequently with memory and I/Odevices fetch, decode and execute


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Can it responds to unexpected event? While printing,can it stop printing temporarily and read any datathat arrive at the input?

memory response is too slow, can the it wait untilmemory is ready?

P needs to be able to respond to various situations

External devices should be able to interrupt andrequest the attention of the P


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The communication process can categories as:1. Microprocessor initiated operations

2. Peripheral (or externally) initiated operations

Log c c rcu ts, set o s gna s to trans er n ormat on,control signals, clock circuitry


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Microprocessor Operations

1. MPU initiated operations Memory Read: Read data (binary information) from

memory

I/O Read: Accepts data from input devices

I/O Write: Sends data to output devices

2. Peripheral initiated operations

Reset: Start again from the beginning

Interrupt: Stop the ongoing process temporarily

Wait: Delay the MPU operation

Bus Request: Request the use of the buses


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How does the MPU identify a memory or an I/Odevice?

MPU identifies each memory register or I/O by a

How does the MPU inform the peripherals when it is

ready to read or write data? MPU send out appropriate timing signals called

control signals before it transfers data


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Steps of the MPU performs any operation:1. Identify the memory location or the peripheral with

its address

.

3. Read/Transfer binary data


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P Buses and Signals

MPU requires three sets of communication linescalled buses:

Address

a a

Control


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Address Bus

Identifies each peripheral or memory location How large? Depends upon internal design of the

microprocessor


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Generalized MPU

AddressBus

Clock

PowerGround

Am

A0

MPU

The bus is unidirectional thesignals flow from the MPU to

peripherals or memory


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Data Bus

Transfer data between MPU and external devices(memory, I/O)

Determines how large a binary number can be


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Generalized MPU

AddressBus

Clock

PowerGround

Am

A0

MPU

The bus is bidirectional the

signals flow either direction

Data Bus

Dn

D0


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Control Bus

Generated by MPU to indicate its operation Carries commands from the MPU and status signals


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Generalized MPU

AddressBus

Clock

PowerGround

Am

A0

MPU

The bus is unidirectional the

signals flow from the MPU to

peripherals or memory

Data Bus

Dn

D0

Controland Status

Signals


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External Request Signals

Interrupt the ongoing MPU operations Four categories:

Reset

Interrupt Wait

Bus Request


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Generalized MPU

AddressBus

Clock

PowerGround

Am

A0

MPU Data Bus

Dn

D0

Controland Status

Signals

ExternalRequests


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Request Acknowledge Signals

MPU informs the external peripherals that it is readyto accept the request


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Generalized MPU

AddressBus

Clock

PowerGround

Am

A0

MPU Data Bus

Dn

D0

Controland Status

Signals

ExternalRequests

RequestAcknowledge


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Instruction Cycle

Time period during which a microprocessorprocesses instructions from memory

Fetch Decode Execute


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Fetch an Instruction

Microprocessor places a memory address on theaddress bus

Microprocessor reads binary information

A register is used to hold memory addresses

The address in the register is incremented after thefetching process is completed


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Decode an Instruction Microprocessor interprets the instruction

Is it a complete instruction? If not, how many morebytes need to be fetched?

W at type o operat on s requ re an on w at ata? Microprocessor needs an instruction decoder to

perform these operation


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Executing an Instruction Microprocessor performs the data manipulation

The operations can be classified as:

Data copy (transfer)

Arithmetic/logic Decision making

i.e. Subtraction of two numbers

Both numbers are loaded into registers Indicate whether the result is +ve, -ve or zero flag


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MPU Internal Architecture

InstructionDecoder

Flags

MemoryPointer

Registers

InternalBus

eg s ers

ALU


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MPU Architecture

AddressBus

Clock

PowerGround

InstructionDecoder

Data Bus

Controland Status

Signals

ExternalRequests

RequestAcknowledge

Flags

MemoryPointer

Registers

Registers

ALU


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Important Concepts MPU should have the following signals to

communicate with memory and I/O devices

1. Address bus

2. a a us

3. Control signals

4. External request signal

5. Request acknowledge signals

6. Clock and power


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Important Concepts MPU should have the following to process data

internally:

1. Instruction decoder

2. eg s ers

3. Registers as memory pointer

4. ALU

5. Flags


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What is memory? Memory is an essential components of a

microcomputer system that retain digital data

Stores binary instruction and data

Prov es one o t e core unct ons o m crocomputer information retention

Memory classification:

Primary memory

Secondary storage


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Primary memory Main memory or internal memory

Directly accessible to microprocessor

Use for executing and storing programs

Fast enough to keep up with the execution speed Two types of main memory:

Random-access Memory (RAM)

Read-only Memory (ROM)


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RAM P can write into or read from the memory

Use for information that is likely to altered

Volatile contents are destroyed when the power isturne o

Two types of RAM

Static RAM (SRAM)

Dynamic RAM (DRAM)


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ROM P can read only from the memory

Use for programs and data that need not be altered

Non-volatile retains stored information even if thepower s turne o

Five types of ROM

Masked ROM

Programmable ROM (PROM) Erasable Programmable ROM (EPROM)

Electrically EPROM (EEPROM)

Flash Memory


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DRAM Type of RAM that only holds its data if it is

continuously accessed by special logic called arefresh circuit

Refresh circuit reads the contents of each memor

cell, whether the memory cell is being used at thattime or not

If not DRAM will lose its contents dynamic

DRAM is slower than SRAM Require extra circuitry (Refresh circuit)

Made up of one transistor and one capacitor

High density

Cheaper


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SRAM Type of RAM that holds its data without external

refresh, for as long as power is supplied to the circuit

SRAM is faster than DRAM

Does not requ re re res c rcu t

Made up of four to six transistors

Less density

More expensive


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Secondary Storage Not directly accessible by the microprocessor

Use to store data (results after completion ofprogram execution, computation etc.)

Non-vo at e reta ns store n ormat on even t epower is turned off

Typically less expensive than primary memory

Data are kept for longer time

USB flash drive, floppy disk, hard disk, CD, DVD etc.


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Memory cells Exactly one bit

A flip-flop or latch withtri-state buffer

DOUTDIN D Q

EN

/WR

/RD

EN


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4 latches to form

a 4-bit Register


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Memory Decoder


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3-to-8 Decoder


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8-bit Memory using

Two 4-bit Memory


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Problem 3 addressing lines: A0, A1 and A2 Two 8-bit memory chip with 4 registers

How to address?


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Problem 4 addressing lines: A0, A1, A2 and A3 Two 8-bit memory chip with 4 registers

How to address?


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Requirement of Memory ChipA memory requires:

Address lines to identify a memory register

/EN or /CS enables the chip

rea s t e c p

/WR writes the chip

The number of address lines required is determinedby the number of registers

2n = number of register where n is the number ofaddress line

Additional address lines (if available) are used to

enable the chip (/CS)


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Memory Model


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No. of Reg.No. of Add. LinesA chip with 256 registers needs 256 binary numbers

Each address line can assume 2 logic states (0 and 1)

=x

xrepresent the number of address lines needed toobtain 256 binary numbers

2256

2562

2562

loglog

loglog

loglog

=

=

=

x

x

x


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Memory Writes How the MPU writes into memory?

1. Places the 16-bit address on the address bus of thememory location where a byte is to be stored

.

3. Sends the control signal Memory Write to enable theinput buffer of the memory and then stores the byte


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Memory Writes


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Memory Reads How the MPU reads from memory?

1. Places the 16-bit address on the address bus of thememory location from where a byte is to be read

.

output buffer of the memory3. Memory places the data byte on the data bus and the

MPU reads the data byte


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What is I/O? Means through which the MPU communicates with

the outside world

For example:

e accepts nary ata as nput rom ev ces

such as keyboards or mouse

The MPU sends data to output devices such as LEDs orprinter


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Two different methods an MPU identifies I/Odevices:

8 bit address

16 it a ress

I/O with 8 bit Addresses


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I/O with 8-bit Addresses

(Peripheral-Mapped I/O) Uses 8 address lines (low-order address bus) to

identify an input or an output device

Address range from 00H to FFF 256 nput an 256 output ev ces w c are

differentiated by the control signals

I/O Read for input devices

I/O Write for output devices

I/O with 16 bit Addresses


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I/O with 16-bit Addresses

(Memory-Mapped I/O) Uses 16 address lines to identify and I/O device

I/O is connected as if it is a memory register

Uses the same control signals (Memory Read orMemory Wr te


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Microprocessor, Memory & IO

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