This document contains the summary of a session on computer organization and architecture. It discusses asynchronous data transfer methods like strobe control and handshaking. Strobe control uses a single strobe line to time data transfers, while handshaking uses two control signals - one from the source to indicate valid data and another from the destination to acknowledge receipt. It explains source initiated and destination initiated handshaking transfers through state diagrams. The next session will cover modes of transfer.

1. CS304PC:Computer Organization
and Architecture (R18 II(I sem))
Department of computer science and engineering (AI/ML)
Session 25
by
Asst.Prof.M.Gokilavani
VITS
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2. TEXTBOOK:
• 1. Computer System Architecture – M. Moris Mano,
Third Edition, Pearson/PHI.
REFERENCES:
• Computer Organization – Car Hamacher, Zvonks
Vranesic, Safea Zaky, Vth Edition, McGraw Hill.
• Computer Organization and Architecture – William
Stallings Sixth Edition, Pearson/PHI.
• Structured Computer Organization – Andrew S.
Tanenbaum, 4th Edition, PHI/Pearson.
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3. Unit IV
Input-Output Organization: Input-Output
Interface, Asynchronous data transfer, Modes of
transfer, Priority Interrupt Direct memory
Access.
Memory Organization: Memory Hierarchy,
Main memory, Auxiliary memory, Associate
memory, cache memory.
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4. Topics covered in session 25
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•Input-Output Organization
•Input-Output Interface
• Asynchronous data transfer
•Modes of transfer
•Priority Interrupt Direct memory Access.

5. Data Transmission
• Data transmission (i.e., from source to destination )
can be done either Parallel or Serial.
• In Parallel data transmission , the sequence of data
can be transmitted parallel at a time .
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6. Synchronous Data Transfer
• The device which sends
data & the device which
receives data are
synchronized with the
same clock.
Asynchronous Data Transfer
• Data transfer is not based on
the predetermined timing
pattern.
• This technique of data
transfer is used , when the
speed of an I/O device is not
match with the speed of
CPU & the timing
characteristics of I/O device
is not predictable.
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7. Asynchronous Data Transfer
• In a computer system , CPU & I/O interfaces are designed
independently of each other.
• When the internal timing in each unit is independent from the
other and the registers in Interface & registers of CPU uses its
own private clock, Asynchronous data transfer can be used to
coordinate the speed & its timing characteristics.
• The Asynchronous data transfer between two independent units
requires that control signals transmitted between the
communicating units , so that the time can be indicated at which
they send data.
• The Asynchronous way of data transfer can be achieved by two
methods.
» Strobe control
» Handshaking
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8. Strobe Control
• The strobe control method of asynchronous
data transfer employs a single control line to
time each transfer, which is known as strobe.
• It may be achieved either by source or
destination.
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10. • The data bus carries the binary information from source
unit to the destination unit.
• The strobe is a single line that informs the destination
unit when a valid data word is available in the bus.
• The source unit first places the data on the bus.
• After a brief delay (to ensure that the data settle to a
steady value), the source activates the strobe pulse.
• The information of the data bus and the strobe signal
remain in the active state for sufficient time period to
allow the destination unit to receive the data.
• The source removes the data from the bus for a brief
period of time after it disables its strobe pulse.
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12. • The destination unit activates hr strobe pulse ,
informing the source to provide the data.
• The source unit responds by placing the required
binary information on the unit to accept it.
• The data must be valid and remain in the bus long
enough for destination unit to accept it.
• The falling edge of strobe pulse can be used again
to trigger a destination register.
• The destination unit then disables the strobe.
• The source removes the data from the bus after a
predetermined time interval.
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13. Disadvantage of strobe method
• The source unit that initiates the transfer has
no way of knowing whether the destination
unit has actually received the data item that
was placed in bus.
• The destination unit that initiates the transfer
has no way knowing whether the source unit
has actually placed the data on the bus.
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14. Handshaking Method
• The Handshaking method solves the problems raised
in strobe method, by introducing a second control
signal that provides a reply to the unit that initiates
the transfer.
• The data transfer can be occur as
• Source initiated Transfer
• Destination initiated Transfer
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15. Source Initiated transfer using
Handshake
• The Two Handshaking lines generated from
the source are,
– Data Valid - Source to Destination to inform,
whether there are valid data in the bus.
– Data Accept -Destination to source to inform,
whether it can accept data.
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18. The sequence of events shows the four possible states
that the system can be at given time
• The source unit initiates the transfer by placing
the data on the bus and enabling its data valid
signal.
• The data accepted signal is activated by the
destination unit after it accepts the data from the
bus.
• The source unit then disable its data valid signal ,
which invalidates the data on the bus.
• The destination unit disable its data accepted
signal and the system goes into its initial state.
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19. The destination initiated transfer
using handshaking
• The two handshaking lines in this scheme are
• Data valid
• Ready for data
• The source unit in this case, does not place data on the
bus until after it receives the ready for data signal from
the destination unit.
• The handshaking procedure follows the same pattern as in
source initiated except the read for data signal has been
converted from data accepted in case of source initiated.
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22. Topics to be covered in next session 26
• Modes of transfer
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Thank you!!!