Synchronous and asynchronous reset in sequential circuits..

1. SYNCHRONOUS AND
ASYNCHRONOUS RESET
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2. WHY RESET IS USED..?
 Reset is used to initialize the hardware design of
a system and to make system to known state from
unknown state.
Ex…RESET SIGNAL
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3. TYPES OF RESETS….
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 Reset is of two types :-
1. Synchronous reset :-- a synchronous reset will reset
the circuit at active edge of clock .

4. ADVANTAGES OF
SYNCHRONOUS RESET….
 Gives a completely synchronous circuit
 Provides filtering for the reset signal, So circuit will
not be affected by glitches.
 Will meet reset recovery time, as the deassertion will
happen within 1 clock cycle
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5. DISADVANTAGES…
 Reset needs to be stretched, if it is not long
enough to be seen at the active clock edge.
 Requires presence of clock to reset the circuit.
 Asynchronous reset may be required if there are
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internal tri state buffers.

6. DISADVANTAGES….
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 It is slow.
 Synthesis will not be able to easily differentiate reset
from other signals. So this has to be taken care while
doing synthesis. Otherwise it may lead to timing
issues.
 If there are gated clocks for power saving, this type of
reset won’t be suitable.

7. ASYNCHRONOUS RESET….
2. Asynchronous reset :-- asynchronous reset will reset
the circuit asynchronously i.e no matter with the
clock.
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8. ASYNCHRONOUS RESET
ADVANTAGES ….
 Reset gets the highest priority.
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 It is fast.
 Does not require presence of clock to reset the circuit.

9. DIADVANTAGES…
 Reset line is sensitive to glitches.
 May have metastability issues
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10. THANK YOU
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