Lecture 14 Flashcards
Describe sequential logic circuits
-Sequential Logic Circuits build on combinational logic circuits.
-The output from a combinational logic circuit only depends upon the input at any time
-However, the sequential logic circuit has the memory element.
-Hence, the sequential logic circuit, their output does not only depend upon the input state at a particular time but also upon the previous input state
How is feedback given in sequential circuits?
They are dependent on past input along with present input, so feedback is given in the form of a feedback loop. Feedback loop is the memory element of the sequential system
What are the two types of circuits in sequential circuits? and describe them.
Event-driven aycnhronous circuits that change state immediately when enabled and or when driven by pulses of inputs
clock-driven, synchchronous circuits that are synchronized to a specific clock signal
Describe “Flip Flop” and state the conditions in which they work.
It is a sequential system which has two stable sides and it flips between the two.
Flip Flop under these conditions:
-Have 2 distinct states (Current state and previous state)
-Remain in one state until instructed to change
-Can change rapidly from one state to hte other and the state value ( 0 or 1 ) must be clearly shown.
How does the SR flip-flop work?
The most basic sequential system is called a ‘flip-flop’ (or ‘bistable’).
It has two stable states (hence ‘bistable’) and it flips (or flops) between the two.
A flip-flop is working under the conditions below:
Have two distinct states (current state and previous state).
Remain in one state until instructed to change.
Can change rapidly from one state to the other, and the state value (0 or 1) must be clearly shown.
Describe the SR Flip-Flop with a negative pulse
Set SR flip-flop uses two cross-coupled NAND gates
-SET the devicde ( meaning the output will be 1 ) and one will RESET the device ( meaning the output will be 0 )
-Commonly used in memory circuits as one-bit memory device
The basic SR Flip-Flop with a positive pulse
Uses positive pulse SR flip-flop uses two cross-coupled NAND gates plus inverters at both inputs
