INPUT AND OUTPUT

   Input and output

 Introduction

     In this blog I will discuss on input/output procedures&devices .External device are not generally connected directly int the bus structure of the computer.I/O module is an interface for the external devices (peripherals) to CPU and memory.

Input device

• Mouse

• ScanKeyboardner

• CD-Rom

• Game Controller

 

Output device

• Monitor

• Printers

• Disk Drive

• Floppy Drive

• CDRW-Rom

• Speakers

 

External device

• Modem

• NIC

• MONITOR

 

A model i/o configuration

Function of I/O modules

• Control and Timing. 

• CPU Communicating. 

• Device Communication. 

• Data Buffering. 

• Error Detection.

Control and Timing

• CPU asks I/O module to check the status of attached device. 

• I/O module tells the status. 

• CPU requests for data transfer to I/O module if device is ready. 

• I/O module gathers the data and transfers to the CPU.

Cpu Communication

• Command Decoding : Like read/write seek etc. Data 

Exchange between CPU and Module. Status reporting to CPU, since 

peripherals are slow. Address recognition for the devices connected 

to it. 

Device Communication

• Device Communication : This may involves command, status 

information and data transfer. 

Data Buffering

• Data Buffering :  Essential function to overcome speed mismatch. 

Error Detection.

• Error Detection : Like paper jam, bad data etc.

TECHNIQUES OF I/O

• Programmed I/O : The CPU issues a command then waits for I/O 

operations to be complete. The CPU is faster than the I/O module 

then method is wasteful. 

• Interrupt Driven I/O : The CPU issues commands then proceeds 

with its normal work until interrupted by I/O device on completion 

of its work. 

• DMA : In this CPU and I/O Module exchange data without 

involvement of CPU. 

• Memory mapped I/O : Memory and I/O are treated as memory 

only. It means no signal like IO/M. 

Isolated I/O  : Address space of memory and I/O is isolated. 

It uses IO/M  signal

Interrupts l/0

• CPU interrupt request line triggered by I/O devices

• Interrupt handler receives interrupt

• Maskable to ignore or delay some interrupts

• Interrupt vector to dispatch interrupt to correct handler

Based on priorty

Some unmaskable

• Interrupt mechanism also used for exceptions

Interrupt Processing

Interrupt driven I/O cycle

Evolution OF The I/O Funtion

1) CPU directly controls a peripheral device.
2) Use controller or i/o module.
3) Implement interrupts.
4) i/o module is given direct access to memory via DMA
5) i/o module is enhanced to become a processor
6) i/o module has a local memory of its own


Direct Memory Access

• Special Purpose Processor: DMA controller
• Free CPU from pure data transfer tasks
• DMA access: Pointer to source, destination and size of data issued to start transfer
• Processor writes the data DMA access data and continuous working
• Handshake protocol
• DMA request and DMA acknowledge
• DMA controllers are standard components in PCs
• Bus-mastering I/O hardware contain their own DMA hardware

DMA function

• Additional modul (hardware) on bus
• DMA controller takes over from CPU for I/O

DMA Transfer

I/O Transfer Mode

Serial
o In band signaling
o Bit oriented
o Bit/byte word translation

Parallel
o Byte word oriented
o Out of band signaling
o IDE, SCSI



SERIAL TRANSFER

• Asynchronous Clocking
o Master clock the transfer
o Slave derive clock from master

• Synchronous clocking
o Independent clocking
o Verification by synchronization pattern

PARALLEL TRANSFER

• Data transfer
o Read sector
o Write sector

• Control
o Disk seek

• Transfer Integrity
o Transfer parity
o Data encoding