Asynchronous transfer is a method of data communication that allows devices operating at different speeds to exchange information without relying on a shared clock. This technique is essential for reliable communication between components such as CPUs, keyboards, and printers, which often operate at varying speeds. The document explains the concept of handshaking, a coordination process that signals when data is ready to be sent and received. It also discusses the advantages and disadvantages of asynchronous transfer, making it relevant for students and professionals in computer science and engineering. Key applications include keyboard input, serial communication, and peripheral device interaction.

Key Points

  • Explains asynchronous transfer as a method for reliable data communication between devices with different speeds.
  • Describes handshaking as a coordination process that signals data readiness and completion.
  • Highlights applications in keyboard input, serial communication, and peripheral device communication.
  • Discusses advantages such as independence from a common clock and reliability in data transfer.
Ekemini Tom
10 pages
Language:English
Type:Presentation
Computer Science
Ekemini Tom
10 pages
Language:English
Type:Presentation
Computer Science
344
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Asynchronous Transfer
INTRODUCTION
IN COMPUTER SYSTEMS, DATA TRANSFER DOES NOT ALWAYS HAPPEN
BETWEEN DEVICES OPERATING AT THE SAME SPEED. WHILE THE CPU WORKS
VERY FAST USING A CLOCK, MANY EXTERNAL DEVICES SUCH AS
KEYBOARDS, PRINTERS, AND DISKS OPERATE AT DIFFERENT AND OFTEN
UNPREDICTABLE SPEEDS. ASYNCHRONOUS TRANSFER IS A METHOD THAT
ALLOWS DATA TO BE TRANSFERRED RELIABLY BETWEEN SUCH DEVICES
WITHOUT REQUIRING A COMMON CLOCK.
THE WORD ASYNCHRONOUS MEANS ‘NOT OCCURRING AT THE SAME
TIME’ OR ‘NOT SYNCHRONIZED BY A COMMON CLOCK.’ SYNCHRONOUS
TRANSFER USES A SHARED CLOCK, AND ASYNCHRONOUS TRANSFER DOES
NOT USE A SHARED CLOCK. IN ASYNCHRONOUS TRANSFER, THE SENDER
AND RECEIVER DO NOT RELY ON CLOCK PULSES TO DECIDE WHEN DATA IS
VALID.
IN REAL SYSTEMS, NOT ALL COMPONENTS CAN BE FORCED TO RUN AT
THE SAME CLOCK SPEED. THE CPU MAY RUN AT GIGAHERTZ SPEEDS,
WHILE A KEYBOARD OR PRINTER OPERATES THOUSANDS OR MILLIONS OF
TIMES SLOWER. CPU, KEYBOARD, PRINTER, EXTERNAL STORAGE (FLASH),
SERIAL DEVICES. IF SYNCHRONOUS TRANSFER WERE TO BE USED, SLOWER
DEVICES WOULD EITHER LOSE DATA OR FORCE THE CPU TO WAIT
UNNECESSARILY.
ASYNCHRONOUS TRANSFER IS LIKE A CONVERSATION BETWEEN TWO
PEOPLE WITHOUT A METRONOME OR STOPWATCH. ONE PERSON SPEAKS
WHEN HE’S READY. THE OTHER LISTENS WHEN READY. THEY DON’T RELY
ON TIMING, THEY RELY ON SIGNALS LIKE “ARE YOU READY?” OR “I’VE
HEARD YOU”. SYNCHRONOUS MARCHING SOLDIERS STEPPING
TOGETHER. ASYNCHRONOUS TWO PEOPLE AGREEING VERBALLY.
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FAQs

What is asynchronous transfer in computer systems?
Asynchronous transfer is a method that allows data to be transferred reliably between devices operating at different speeds without requiring a common clock. This means that the sender and receiver do not rely on clock pulses to determine when data is valid. Instead, it uses control signals to coordinate data movement, ensuring that communication can occur even when devices operate at unpredictable speeds.
How does handshaking work in asynchronous transfer?
Handshaking is a coordination method in data transfer where the sender and receiver use control signals to indicate readiness and completion of data transfer. In asynchronous transfer, the sender activates a request signal to indicate that data is ready, while the receiver acknowledges this by activating an acknowledge signal. This process ensures reliable communication without the need for a shared clock, allowing both devices to operate independently.
What are the advantages of asynchronous transfer?
Asynchronous transfer has several advantages, including the fact that it does not require a common clock, allowing devices to operate independently. It is particularly effective with slower devices, as the CPU does not assume timing, ensuring reliable data transfer only occurs when both sides are ready. Additionally, it reduces timing errors because strict synchronization is not needed.
What are the disadvantages of asynchronous transfer?
The main disadvantages of asynchronous transfer include being slower than synchronous transfer due to the overhead introduced by handshaking. It also requires more control signals, such as request and acknowledge lines, which adds complexity to the system. Furthermore, the control logic becomes more complex compared to simpler clock-based systems, making implementation more challenging.
What applications commonly use asynchronous transfer?
Asynchronous transfer is commonly used in various applications including keyboard input, mouse input, serial communication, UART, peripheral interfaces, and external device communication. Most I/O devices rely on asynchronous transfer due to their unpredictable speeds, such as keyboards, where user typing speed can vary significantly.
How is asynchronous transfer compared to synchronous transfer?
Asynchronous transfer differs from synchronous transfer primarily in that it does not use a shared clock. While synchronous transfer relies on a common clock to coordinate data transfer, asynchronous transfer uses control signals and handshaking to ensure reliable communication. Although asynchronous transfer is generally slower, its flexibility and reliability make it essential for communication between devices operating at different speeds.
Can you give an example of asynchronous transfer?
An example of asynchronous transfer can be likened to a conversation between two people without a timer. One person speaks when ready, and the other listens when ready, relying on signals of readiness rather than strict timing. Another simpler analogy is that of package delivery, where the sender places a package at the door (request), and the receiver collects it (acknowledge) without a predetermined schedule.

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