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