Logic Lesson 11
Synchronous sequential circuit
Circuit whose behavior can be defined from the knowledge of its signals at discrete instants of time
Asynchronous sequential circuit
Depends upon the input signals at any instant of time and the order in which the inputs change
External inputs
Determine the condition for changing the state in the storage elements
Outputs
Function not only of the inputs, but also of the present state of the storage elements
Asynchronous sequential circuit
Gate-type asynchronous systems, the storage elements consist of logicgates whose propagation delay provides the required storage
Asynchronous sequential circuit
Internal propagation delay of logic gates is sufficient duration to produce the needed delay, so that actual delay units may not be necessary
D latch
One way to eliminate the undesirable condition of the indeterminate state in the SR latch is to ensure that inputs S and R are never equal to 1 at the same time which is done by ___________________
Combinational logic gate or circuit
Receives binary information from external inputs, along with the present state of the storage elements which describes the binary value of the outputs
Trigger
State of a latch or flip-flop is switched by a change in the control input. and this momentary change is called a _____________
Asynchronous sequential circuit
Storage capability of a time-delay device varies with the time it takes for the signal to propagate through the device
Toggle
T flip-flop (T stands for ____________ )
sequential logic circuits
Type of logic circuit that employs memory element in addition to combinational logic gates, whose outputs are a function of the inputs and the state of the memory element
Level Clocking
Type of synchronous sequential circuit that uses clock pulse in theinputs of memory elements
Clocked sequential circuits
Use clock pulses to control storage elements are called _______________
Flip-flop
Used in clocked sequential circuits are called _________________
Master-slave d flip-flop
also called negative edge-triggered d flip-flop
Clock pulses
are a square wave signal that is sent to each memory elements (flip-flop)
Latches
are said to be level sensitive devices
Latches
are useful for storing binary information and for the design of asynchronous sequential circuits
Storage (or memory) elements
circuits that are capable of storing binary in formation at any given time defines the state of sequential circuit
Transparent latch
d latch is also called _________________
Bi-stable circuit
has two complementary outputs that can assume either of the two logic levels 0 or 1.
latch or flip-flop
is a bi-stable circuit that is most often used in applications that require data storage.
Flip-flop
is a binary storage device capable of storing one bit of information which in a stable state
SR latch
is a circuit with two cross-coupled NOR gates or two cross-coupled NAND gates, and two inputs labeled S for set and R for reset.
Synchronization
is achieved by a timing device which provides a clock signal having the form of a periodic train of clock pulses
sequential logic circuits
needed for storing information between operations.
Next state
of the storage elements is also a function of external inputs and the present state
Bubble
outside the block adjacent to the dynamic indicator designates a negative edge for triggering the flip-flop circuit while absence of a bubble indicates that circuit is a positive-edge triggered D flip-flop.
Dynamic indicator (>)
represents the flip-flop responds only during edge transition of the clock.
PRESET
set switch input sets the flip-flop output (Q) to 1
PRECLEAR
simply clear switch input clears the flip-flop output (Q) to 0
Clock Generator
synchronization is achieved by a timing device called a ________________
Edge-Triggering
synchronous sequential circuit output that can only be changed on the rising or falling edge of the clock.
Time-delay devices
Storage elements commonly used in asynchronous sequential circuits are ____________.
Flip-flop
are edge-sensitive devices
JK flip-flop
versatile of the basic flip-flops specially in the design of digital counter circuit.
T flip-flop
when it is enabled, its outputs change state every time a clock pulse is applied to the input