Different Types of Flip-Flops in Digital Systems
Explore various flip-flop types including SR latch, JK flip-flop, T flip-flop, and understand their characteristic tables and operations. Learn about SR latch with NOR and NAND gates, utilize JK flip-flop to avoid undefined states, and discover how T flip-flop works as a toggle FF equivalent to JK FF.
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ECE 352 Digital System Fundamentals Other Flip-Flop Types Other Flip-Flop Types 1 1
Other Latch and FF Types You do not need to memorize how these other latch/flip-flop types work for this class You should know that they exist (sometimes companies ask about them during job interviews) The behavior of a flip-flop is described using a characteristic table The table indicates how it responds to the input(s) Given a characteristic table for a flip-flop, you do need to understand how it works and be able to use it to implement an FSM Even if you have never seen that FF type before! Other Flip-Flop Types 2 2
SR Latch (NOR) S refers to set , R refers to reset S Q Other Flip-Flop Types NOR SR Latch Characteristic Table Inputs Next State Q(t+1) S R R Operation R 0 0 0 1 Q(t) 0 Hold (no change) Reset Q 1 0 1 Set 1 1 ??? Undefined S 3 3
SR Latch Timing Waveform The Q and Q outputs are both unknown until S and R are known When S = R = 1, Q = Q = 0! If we try to hold afterwards with S = R = 0, the value in the latch oscillates R Q Other Flip-Flop Types S S R Q 4 4
SR Latch (NAND) Can make an S R latch with NANDs Inputs become active-low S Q Other Flip-Flop Types NAND Latch Characteristic Table Inputs Next State Q(t+1) 0 0 ??? 0 1 1 R Operation Undefined Set Q 1 0 0 Reset 1 1 Q(t) Hold (no change) 5 5
JK Flip-Flop Based on SR latches J S, K R Avoids the undefined case! Other Flip-Flop Types JK Flip-Flop Characteristic Table Inputs Next State Q(t+1) J K J K Q Operation 0 0 0 1 Q(t) 0 Hold (no change) Reset 1 0 1 Set 1 1 Complement (t) 6 6
T Flip-Flop Toggle FF is equivalent to JK FF with J=K=T MUST have a set or reset input to start at a known initial value Other Flip-Flop Types T Flip-Flop Characteristic Table Input Next State Q(t+1) T PRN T Q Operation 0 Q(t) Hold (no change) CLRN 1 Complement (t) 7 7
Using Other Flip-Flop Types Create state table as usual But Next State no longer equal to the FF input That was only the case because a D flip-flop s next state is equal to its D input! Add extra column(s) for the flip-flop input(s) For each row of the state table, determine which FF input value(s) will cause the flip-flop to enter the required next state Refer to the flip-flop s characteristic table Create the combinational logic for the FF inputs and the circuit output Other Flip-Flop Types 8 8
Example: Make D from JK Express DFF behavior using a state diagram Create a state table from the state diagram 1 1 Input: D Output: Q 0 1 0 1 Other Flip-Flop Types 0 0 D is not the next state in this case it is the input! Input D 0 0 1 1 Curr State Q 0 1 0 1 Next State N 0 0 1 1 The output is equal to the current state, so we are not showing it separately 9 9
Example: Make D From JK Add columns for the JK flip-flop inputs Calculate these values for each row based on the current state and the desired next state Refer to the characteristic table to see what input values make the required transition happen Other Flip-Flop Types Curr State Q 0 1 0 1 Next State N 0 0 1 1 FF JK Characteristic Table Input Inputs J K 01 or 00 or 11 01 10 10 or 00 Inputs Next State Q(t+1) D 0 0 1 1 J K 0 0 Q(t) 0 1 0 or 11 1 0 1 1 1 (t) 10 10
Example: Make D From JK Add columns for the JK flip-flop inputs Calculate these values for each row based on the current state and the desired next state Refer to the characteristic table to see what input values make the required transition happen Other Flip-Flop Types Take advantage of the multiple options by using don t-cares! Curr State Q 0 1 0 1 Next State N 0 0 1 1 FF Input Inputs J K 01 or 00 or 11 01 10 10 or 00 D 0 0 1 1 JK = 0X JK = X1 JK = 1X JK = X0 or 11 11 11
Example: Make D From JK Create the required logic based on the state table J Q 0 1 X D Other Flip-Flop Types 0 0 D J K Q Q 1 J = D X 1 CLK K Q 0 1 1 D D = 0 J = 0, K = 1 (reset) D = 1 J = 1, K = 0 (set) 0 X X K = D 0 1 12 12
Example: Make JK From D Express JK behavior using a state diagram Create a state table 10, 11 00, 10 Inputs: J K Output: Q 0 1 0 1 Other Flip-Flop Types 00, 01 Input J K 0 0 (hold) 0 1 (reset) 1 0 (set) 1 1 (toggle) Curr State Q 0 1 0 1 0 1 0 1 01, 11 Next State D 0 1 0 0 1 1 1 0 JK Characteristic Table Inputs Next State Q(t+1) J K 0 0 Q(t) 0 1 0 1 0 1 1 1 (t) 13 13
Example: Make JK From D Create the required logic based on the state table D K Q 00 01 0 11 0 10 0 J Other Flip-Flop Types 1 0 D = J Q + KQ 1 1 0 1 1 J K D Q Q Using Q output CLK 14 14
ECE 352 Digital System Fundamentals Other Flip-Flop Types Other Flip-Flop Types 15 15
