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1. CS-’A’
ASYNCHRONOUS DATA
TRANSFER
Guided By: Submitted By:
Mrs. Rupali Bhartiya Navin Kumar Sharma
Roll no.:0802CS143D02
SHRI VAISHNAV INSTITUTE OF
TECHNOLOGY & SCIENCE, INDORE

2. INTRODUCTION

3. Introduction
• Asynchronous data transfer between two
independent units requires that control signals
be transmitted between the communicating
units to indicate the time at which data is being
transmitted

4. Two Asynchronous Data Transfer Methods
• Strobe pulse:
• A strobe pulse is supplied by one unit to indicate
the other unit when the transfer has to occur
• Handshaking
• A control signal is accompanied with each data being
transmitted to indicate the presence of data The
receiving unit responds with another control signal to
acknowledge receipt of the data

5. STROBE CONTROL
• Employs a single control line to time each
transfer
• The strobe may be activated by either the
source or the destination unit

6. Source
Unit
Destination
Unit
Data bus
Strobe
Strobe
Data
Valid data
a) Block diagram
b) Timing diagram
Source-Initiated Strobe for Data Transfer

7. Destination-Initiated Strobe for Data Transfer
Source
Unit
Destination
Unit
Data bus
Strobe
Strobe
Data
Valid data
a) Block diagram
b) Timing diagram

8. HANDSHAKING
• Strobe Methods
• Source-Initiated
• The source unit that initiates the transfer has no way of knowing whether
the destination unit has actually received data
• Destination-Initiated
• The destination unit that initiates the transfer no way of knowing whether
the source has actually placed the data on the bus
• To solve this problem, the HANDSHAKE method introduces a second
control signal to provide a Replay to the unit that initiates the transfer

9. SOURCE-INITIATED TRANSFER USING
HANDSHAKE
Block Diagram
Source
unit
Destination
unit
Data valid
Data bus
Data accepted

10. Timing Diagram

11. Sequence of Events

12. • Allows arbitrary delays from one state to the
next
* Permits each unit to respond at its own data
transfer rate
* The rate of transfer is determined by the
slower unit

13. DESTINATION-INITIATED TRANSFER
USING HANDSHAKE
Block Diagram
Source
unit
Destination
unit
Data valid
Data bus
Ready for Data

14. Timing Diagram

15. Sequence of Events

16. ASYNCHRONOUS SERIAL
TRANSFER
• The transfer of data between two units my be done in
parallel or serial.
• In parallel data transmission, total message is transmitted at
the same time. In serial data transmission, each bit in the
message is sent in sequence one at a time.
• 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.

17. Start
bit
Stop
bit
Character bits
1 1 1 1
0 0 0 0
ASYNCHRONOUS SERIAL
TRANSFER

18. • 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 is always a 1.

19. The End
Thank You