Flip Flop www.ustudy.in

Introduction A flip-flop is a semiconductor device that has a digital output which can be toggled between two stable states by providing it with the appropriate digital input signals. www.ustudy.in

Flip Flop Circuit diagram www.ustudy.in

Flip-Flopping Once the output is put in one state, it remains there until a change in the inputs causes it to toggle again. This toggling between two logic states is also referred to as 'flip-flopping'  www.ustudy.in

Types of Flip flop RS Flip-flop D Flip-flop T Flip-flop JK Flip-flop Master Slave Flip-flop Edge Triggered Flip-flop www.ustudy.in

RS Flip Flop SR flip-flop (Or "RS flip-flop") A "set/reset" flip-flop in which activating the "S" input will switch it to one stable state and activating the "R" input will switch it to the other state. www.ustudy.in

Animation of RS Flip Flop Working www.ustudy.in

Truth Table of RS Flip Flop www.ustudy.in

Working of RS Flip Flop The outputs of a basic SR flip-flop change whenever its R or S inputs change appropriately. A clocked SR flip-flop has an extra clock input which enables or disables the other two inputs. www.ustudy.in

Cont., When they are disabled the outputs remain constant. If we connect two clocked SR flip-flops so that the Q and /Q outputs of the first, "master" flip-flop drive the S and R inputs of the second, "slave" flip-flop, and we drive the slave's clock input with an inverted version of the master's clock, then we have an edge-triggered RS flip-flop. www.ustudy.in

Cont., The external R and S inputs of this device are latched on one edge (transition) of the clock (e.g. the falling edge) and the outputs will only change on the next opposite (rising) edge. If both R and S inputs are active (when enabled), a race condition occurs and the outputs will be in an indeterminate state. www.ustudy.in

D Flip Flop The edge-triggered D flip-flop is easily derived from its RS counterpart. The only requirement is to replace the R input with an inverted version of the S input, which thereby becomes D. This is only needed in the master latch section; the slave remains unchanged. www.ustudy.in

D Flip Flop diagram www.ustudy.in

D Flip Flop Characteristic table   Q     Q+     Operation   Reset 1 Set www.ustudy.in

Working of a D Flip Flop One essential point about the D flip-flop is that when the clock input falls to logic 0 and the outputs can change state, the Q output always takes on the state of the D input at the moment of the clock edge. This was not true of the RS and JK flip-flops. www.ustudy.in

Cont., The RS master section would repeatedly change states to match the input signals while the clock line is logic 1, and the Q output would reflect whichever input most recently received an active signal. www.ustudy.in

Cont., The JK master section would receive and hold an input to tell it to change state, and never change that state until the next cycle of the clock. This behavior is not possible with a D flip-flop. www.ustudy.in

Truth table of D Flip Flop  SET and RESET are two additional inputs www.ustudy.in

T Flip Flop The T or "toggle” flip-flop changes its output on each clock edge, giving an output which is half the frequency of the signal to the T input. www.ustudy.in

Cont., It is useful for constructing binary counters, frequency dividers, and general binary addition devices. It can be made from a J-K flip-flop by tying both of its inputs high. www.ustudy.in

T Flip Flop www.ustudy.in

T Flip Flop characteristic table   Q     Q+     Operation   Hold 1 Toggle www.ustudy.in

Cont., The T flip flop has two possible values. When T = 0, the flip flop does a hold. A hold means that the output, Q is kept the same as it was before the clock edge. www.ustudy.in

Cont., When T = 1, the flip flop does a toggle, which means the output Q is negated after the clock edge, compared to the value before the clock edge. www.ustudy.in

Cont., Thus, in a T flip flop, you can either maintain the current state's value for another cycle, or you can toggle the value (negate it) at the next clock edge. www.ustudy.in

Truth table of T Flip Flop www.ustudy.in

JK Flip Flop A JK flip-flop has two inputs similar to that of RS flip-flop. The two inputs of JK Flip-flop is J (set) and K (reset). A JK flip-flop is nothing but a RS flip-flop along with two AND gates which are augmented to it. www.ustudy.in

JK Flip Flop www.ustudy.in

JK Flip Flop Truth table www.ustudy.in

Working of JK Flip Flop When J=K=0 When both J and K are 0, the clock pulse has no effect on the output and the output of flip-flop is same as its previous value. This is because when both the J and K are 0, the output of their respective AND gate becomes 0. www.ustudy.in

Cont., When J=0, K=1 When J=0, the output of the AND gate corresponding to J becomes 0(i.e.) S=0 and R=1. Therefore Q’ becomes 0. This condition will reset the flip-flop. This represents the RESET state of Flip-flop. www.ustudy.in

Cont., When J=1, K=0 In this case, the AND gate corresponding to K becomes 0(i.e.) S=1 and R=0. Therefore Q becomes 0. This condition will set the Flip-flop. This represents the SET state of Flip-flop. www.ustudy.in

Cont., When J=K=1 Consider the condition when CP=1 and J=K=1. This condition will cause the output to complement again and again. This complement operation continues until the Clock pulse goes back to 0. www.ustudy.in

Master slave Flip Flop A master-slave flip-flop is constructed from two flip-flops. One circuit serves as a master and the other as a slave, and the overall circuit is referred taps a master-slave flip-flop. www.ustudy.in

Master slave flip flop www.ustudy.in

Cont., It consists of a master flip-flop, a slave flip-flop and an inverter. Both the flip-flops are positive level triggered, but inverter connected at the clock input of the slave flip-flop forces to trigger at the negative level. www.ustudy.in

Timing relationship of master and slave Flip Flop www.ustudy.in

Truth table of master and slave Flip Flop www.ustudy.in

Edge triggered Flip Flop An edge-triggered flip-flop changes states either at the positive edge (rising edge) or at the negative edge (falling edge) of the clock pulse on the control input.   www.ustudy.in

Edge triggered Flip Flop www.ustudy.in

Types of Edge triggered Flip Flop The three basic types are introduced here:  Edge triggered S-R Flip flop Edge triggered J-K Flip flop Edge triggered D Flip flop www.ustudy.in

Edge triggered S-R Flip flop The operation and truth table for a negative edge-triggered flip-flop are the same as those for a positive except that the falling edge of the clock pulse is the triggering edge. www.ustudy.in

Edge triggered S-R Flip flop As S = 1, R = 0.  Flip-flop SETS on the rising clock edge. www.ustudy.in

Truth table www.ustudy.in

Timing diagram www.ustudy.in

Edge triggered JK Flip flop The J-K flip-flop works very similar to S-R flip-flop.   The only difference is that this flip-flop has NO invalid state.   The outputs toggle (change to the opposite state) when both J and K inputs are HIGH. www.ustudy.in

Truth table www.ustudy.in

Edge triggered D Flip flop The operations of a D flip-flop is much more simpler.  It has only one input addition to the clock.   It is very useful when a single data bit (0 or 1) is to be stored.   www.ustudy.in

Cont., If there is a HIGH on the D input when a clock pulse is applied, the flip-flop SETs and stores a 1.  If there is a LOW on the D input when a clock pulse is applied, the flip-flop RESETs and stores a 0.   www.ustudy.in

Cont., The truth table below summarize the operations of the positive edge-triggered D flip-flop.   As before, the negative edge-triggered flip-flop works the same except that the falling edge of the clock pulse is the triggering edge. www.ustudy.in

Cont., www.ustudy.in

M.S.P.V.L POLYTECHNIC COLLEGE, Thank you M.S.P.V.L POLYTECHNIC COLLEGE, PAVOORCHATRAM. www.ustudy.in