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PART 3:UNDERSTAND I/O IN COMPUTER SYSTEM - Coggle Diagram
PART 3:UNDERSTAND I/O IN COMPUTER SYSTEM
LEARNING OUTCOMES:
by the end of this topic,you should be able to:
define I/O module
draw the I/O module diagram
list I/O devices
describe the I/O bus and interface modules.
I/O MODULE
the term I/O is used to describe any program,operation or device that transfer data to or from a compiter and to or from peripheral device.
every transfer is an output from one device and an input into another.
devices such as keyboards and mouses are input-only devices such as printers are output-only.a writable CD-ROM is both an input and an output device.
I/O MODULE FUNCTION
acts as an interface with the CPU and memory via the system bus or central switch.
acts as an interface with one or kore peripheral devices by tailored data links.
INPUT/OUTPUT DATA TRANSFER
-ASYNCHRONOUS SERIAL TRANSFER
asynchronous serial transmission is character oriented.
each character transmitter consists of a start bit,character bits,and stop bits.
the first bit is called the start bit.it is always a 0 and is used to indicate the beginning of a character.
the last bit called the stop bit always a 1.in asynchronous transmission,binary information is sent only when it is available and the line remains idle when there is no information to be transmitted.
ASYNCHRONOUS COMMUNICATION INTERFACE.
is the transmission of data without the use of an external clock signal,where data can be transmitted continously rather than in a steadt stream.
the most significant aspect of asynchronous communications is variable bit rate,or that the transmitter and receiver clock geneators do not have to be exactly synchronized
CHARACTERISTIC OF ISOLATED AND MEMORY MAPPED I/O
isolated I/O uses a special class of CPU instructions specifically for performing I/O.this is generally found on intel microprocessors,specially the IN and OUT instructions which can read and write one to four bytes (outb,outw,outl) to an I/O device.
the processor and the I/O device have different memory located to each other.
memory mapped I/O is one where the processor and the I/O device share the same memory location (memory).
CHARACTERISTIC OF ISOLATED AND MEMORY MAPPED I/O
MEMORY MAPPED I/O
devices and memory share an address space
I/O looks just like memory read/write
no special commands for I/O
large selection of memory access commands available
ISOLATED I/O
separate address spaces
need I/O or memory select lines
special commands for I/O
limited set
TRANSFER MODE
programmed I/O
interrupt-initiated I/O
direct memory access
PROGRAMMED I/O
is the method of transferring data between the CPU and a peripheral such as a network adapter or an ATA storage device.
in general,programmed I/O happens when software running on the CPU uses instructions that access I/O address space to perform data transfers to or from an I/O device.
the besr known example of a PC device that uses programmed I/O is the ATA interfaceT
programmed I/O refers to using input and output instructions to transfer data between memory and the registers on a peripheral interface.
data are exchanged between the CPU and the I/O module.
the CPU executes a program that gives it direct control of the I/O operation,including sensing device status,sending a read or write command and transferring data.
when CPU issues a command to I/O module,it must wait until I/O operation is complete.
if the CPU is faster that I/O module,there is wastage of CPU time
ADVANTAGE:
simple to implement
-DISADVANTAGE:
-CPU is tied up for the duration of the transfer while doing a relatively simple task
INTERRUPT-INITIATED I/O
overcomes the processor having to wait long periods of time for I/O modules.
the processor does not have to repeatedly check the I/O module status.
summary:
overcomes CPU waiting
no repeted CPU checking of device
I/O module interrupts when ready
DIRECT MEMORY ACCESS
direct memory access is a method of transferring data between peripherals and memory without using CPU.
sometimes,CPU may not be fast enough to keep up with the peripheral.
in this case a special-purpose processir called a DMA controller (DMAC) can be used to transfer data between memory and I/O devices
DIRECT MEMORY ACCESS CONTROLLER (DMAC)
the DMA controller periodically takes over control ofn the system bus from the CPU.
DMAC generates address,data and control signals to transfer data between memory and I/O devices
DIRECT MEMORY ACCESS (DMA)
for high-bandwidth devices (like disks) interrupt-driven I/O would consume a lot of processor cycles.
DMA- the I/O controller has the ability to transfer data directly to/from the memory without involving the processor.
1.the processor initiates the DMA transfer by supplying the I/O device address,the operation to be performed,the memoryaddress destination/source,the number of bytes to transfer
2.the I/O DMA controller manages the entire transfer (possibly thousand of bytes in length), arbitrating for the bus
when the DMA transfer is complete,the I/O controller interrupts the processor to let it know that the transfer is complete.
there may be multiple DMA devices in one system
processor and I/O controllers contend for bus cycles and for memory.