Data transfer system

1. Master of Computer Application

2. On
Data Transfer Techniques
Presented By:
Name :- Ranjit Kumar
Reg No. :- 0305203010
Sem : - 2nd
Master of Computer Application

4. FORMATS OF DATA TRANSFER
Synchronous Data Transfer: -
Synchronous means “at the same time”.
In this format of data transfer transmitter and receiver device are
synchronized with the same clock pulse.
This type of data transfer format is used in between the devices that
match in speed. This method is invariably used in between memory
and microprocessor as they are compatible.
Asynchronous Data Transfer: -
Asynchronous means “at a regular interval”. In this method data
transfer is not based on predetermined timing pattern in this
technique the status of the IO device is checked by the
microprocessor before the data is transferred. This method is
invariably used in between microprocessor and IO devices.

5. MODES OF DATA TRANSFER
THE MICROPROCESSOR receives or transmits binary data in
either of two mode:-
PARALLEL MODE:- In a parallel mode , the entire
word is transferred at one time .the device commonly used
for data transfer are keyboards seven segment LEDs data
converters and memory.
SERIAL MODE:- In the serial mode , data are
transferred one bit at a time over a single line between
the microprocessors and a peripheral. It is commonly
used with peripherals such as CRT terminals , printers,
cassette tapes and modems for telephone.

6. NEEDS OF DATA TRANSFER SCHEME
A wide variety of IO devices having wide range of speed and
other different characteristics are available .A slow responding IO
device cannot transfer data when microprocessor issues
instruction for it as it takes some time to get ready.
Data codes and formats in peripheral differ from the word
format of in the c.p.u and memory
Transfers rates of peripherals is usually slower than the
transfer rates of c.p.u.
Operating modes of peripheral are different from each other
and each must be controlled so as not to disturb the operation of
each other peripherals connected to c.p.u

7. TYPES OF DATA TRANSFER SCHEME
Different types of data transfer techniques are available which can be
broadly divided into two categories:-
MICROPROCESSOR CONTROLLED :- HERE data transfer is
controlled by microprocessor. Microprocessor is primarily
responsible for data transfer whether from I/o to the c.p.u or to the
memory or vice versa .
DEVICE CONTROLLED:- Here data transfer is controlled by
IO device .data is transferred in between IO device and memory
without the intervention of c.p.u.such a transfer increases rate of
transfer and makes the system more efficient

8. MICROPROCESSOR BASED DATA TRANSFER SCHEME
HERE data transfer is controlled by microprocessor. Microprocessor is
primarily responsible for data transfer whether from I/o to the c.p.u or
to the memory or vice versa .MICROPROCESSOR BASED scheme is
further divided into two parts:-
PROGRAMMED DATA TRANSFER SCHEME
INTERRUPT CONTROL DATA TRANSFER SCHEME

9. PROGRAMMED DATA TRANSFER SCHEME
THESE SCHEME IS controlled by the c.p.u . Data are transferred
from an IO device to the c.p.u or to the memory through c.p.u or vice
versa under the control of programs which are stored in memory.This
programs are executed by the c.p.u and is invariably used when small
amount of data is to be transferred.Here also synchronous and
asynchronous mode of transfer is used.Every data transfer operation
involving an IO device requires the execution of an instruction by the
c.p.u. Typically the transfer is between two programmable registers:-
one a C.P.U register and other attached to the IO device.

10. Issue read command to IO module
Read status of IO module
Check
status
Read word from IO module
Write word into memory
done
Next
instruction

11. TYPES OF PROGRAMMED DATA TRANSFER
UNCONDITIONAL
POLLING
DATA TRANSFER USING READY SIGNAL
DATA TRANSFER WITH HANDSHAKE SIGNAL
DRAWBACK OF PROGRAMMED DATA TRANSFER
SCHEME
 THE programmed IO transfer method is quite insufficient .
Consider a typical computer can execute the two instruction that read
and check status in 1 micro second.
Assume that the input device transfers its data at an average rate of 100 bytes per c.p.u will then check the flag 10000 times between each transfer
 The c.p.u is wasting time while checking the flag instead of doing some
useful work.

12. INTERRUPT DRIVEN DATA TRANSFER
The problem with programmed IO is that c.p.u has to wait
along time for the Io device of the concern to be ready for
reception or transmission of data .The c.p.u while waiting, must
repeatedly interrogate the status of the IO device . As a result the
level of the performance of the entire system is severely degraded.
An alternative is interrupt driven IO data transfer.

13. Issue read command to IO module
Read status of IO module
Check
status
Read word from IO module
Write word into memory
done
Next
instruction
NO
READY
C.P.U-------IO
interrupt
IO----------c.p.u

14. DRAWBACKS OF PROGRAMMED AND
INTERRUPT DRIVEN DATA TRANSFER
The IO transfer rates is limited by the speed by which the
CPU can test and service a device.
The CPU is tied up in managing an IO transfer; a number
of instruction must be executed for each IO transfer.
Consider the transfer of block of data using programmed IO CPU is
dedicated to the task of IO and can move data at a rather high rate at the
cost of doing nothing else.
Interrupt IO frees up the CPU to some extent at the
expense of IO transfer rate never the less both methods have an adverse
impact on CPU activity and IO transfer rate. Hence a more efficient
technique was required and then Device data transfer scheme i.e DMA data
transfer was introduced.

15. DEVICE CONTROL DATA TRANSFER
The transfer of data between the mass storage device and a system
memory is often limited by the speed of microprocessor. Removing
the the microprocessor during such a transfer and letting the
peripheral manage the transfer to or from memory would improve
the speed of transfer and hence will make the system more efficient.
This transfer technique is called DMA Data Transfer.
During DMA transfer processor is idle, so it
has no longer control on the system buses. A DMA Controller takes
over the buses and manage the transfer directly between the
peripheral and the memory. It is fastest scheme then Programmed
Data Transfer Scheme and the CPU regains the control of buses
after data transfer.

16. RAM
RD WR ADD DATA
IO
PERIPHERAL
DEVICE
Interrupt
BG
C.P.U
BR
RD WR ADD DATA
RD WR ADD DATA
DS
RS DMA CONT
BR
BG
INTERRUPT
ADDR
ADDRESS BUS
DATA BUS
DMA
ACK
DMA
READ CONTROL

17. DMA TRANSFER OPERATION
THE c.p.u communicates with the DMA through the address and data buses as with
any interface unit.
The DMA has its own address which activates the DS and RS lines
The c.p.u initializes the DMA through data lines
Once the DMA receives the start control command it can start the transfer
between the peripheral devices and memory.
When the peripheral device sends a DMA request the DMA controller activates the BR line,
informing the c.p.u to relinquish the busses.
The c.p.u responds with its BG lines informing the DMA that its busses are disabled.
The DMA then puts the current value of its address register into the address bus, initiates
the WR or RD signal and then sends the DMA ACK to the peripheral device.
RD and WR lines are bi-directional.
When the peripheral device receives a DMA ACK it puts a word in the data bus or receives a
word from the data bus (for REAWhen BG=0 the RD and WR are input lines,and acts in
master mode and when BG=1 it acts as an output line from the DMA controller to the RAM.
D). Thus the DMA controls the read and write operation and supplies the address for the
memory.

18. TYPES OF D.M.A DATA TRANSFER
THERE are two types of DMA data transfer :-
BURST MODE OF DATA TRANSFER:-A scheme of data transfer , in
which the IO device withdraws the DMA request only after it has
transferred all the bytes. By this technique a block of data is transferred.
It is used mainly in MAGNETIC DISK DRIVES.
CYCLE STEALING MODE OF DATA TRANSFER:- In this
technique a long block of data is transferred by a sequence of DMA
cycle.in this method after transferring one byte or several bytes the IO
device withdraws DMA request. This method reduces interference in
C.P.U ACTIVITIES