Today 3/8/ Lecture 8 Sequential Logic, Clocks, and Displays Flip Flops and Ripple Counters One Shots and Timers LED Displays, Decoders, and Drivers Homework XXXX Reading H&H sections on sequential logic and clocks. Lab If you have questions: Email or call me on my cell (up to pm) Phsx 262 Laboratory Electronics II Spring Lecture 8 Page
Review of Logic Gates AND A B Schematic symbol 2 3 Algebraic example Q Q A B OR A B 2 3 Q Q A B NOT 2 A Q Q A NAND A B 2 74N 3 Q A B Q Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 2
Combinational versus Sequential Combinational logic: Output state of the circuit is dependant only on the present input states. Sequential Logic: Output state depends on both the present input states and on previous history. A Sequential Logic circuit has memory! Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 3
S R RS FF 3 2 4 6 5 NANDs Q Inputs Outputs Q' RS Flip-Flop This circuit cannot be analyzed combinatorially. The output is determined by considering these NAND functions temporally, that is, discussing the state of the outputs (Q and Q ) after some event in terms of (Q and Q ) before. Q S Q' and Q' R Q if S and R then Q S Q ' Q and Q ' R Q Q If Q = NOT(Q ), then state is unchanged. ' The state only changes when one of the inputs (R or S, but not both) are briefly toggled low (FALSE). Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 4
State Table for RS FF Toggle Set input (with R=) S R Q Q Q R Q Q Q S Q Q Q is set high if S goes low No change if both high Toggle Reset input (with S=) Q is reset low if R goes low No change if both high Set S Reset R RS FF 2 4 5 State Table S R QQ?? No Change 3 6 Q Q' Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 5
Data D-type Master-Slave Clocked Flip-Flop D-type RS FFs 3 9 2 8 3 9 2 8 Q 2 4 5 6 2 3 4 5 6 2 3 Q' CLK Master 3 4 Slave Operation: Q=D and Q =not(d) when CLK goes high. No change when CLK is low or goes low, even if D changes No change if D changes after CLK goes high Data is clocked and locked when CLK transition from low to high (Details: http://www.piclist.com/images/www/hobby_elec/e_ckt_6.htm) Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 6
74LS74 Chip-Dual D-type flip-flop with Set and Reset 74LS74 Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 7
Flip Flop Shift Register is clocked in one bit at a time Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 8
Clocked Flip-Flop: Divide by 2 Toggle- Connected Flip-Flop Ambiguous Start Timing Diagram f f/2 Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 9
Clock plus n flip-flops Ripple Counter Divided by 2 Divided by 2 n CLK Clock khz Vcc CLR 2 Q 5 D 3 CP Q 6 4 PR 7474 3 3 CLK2 CLR 2 9 CLK4 CLR 5 CLK8 CLR 2 9 CLK6 2 Q2 2 Q 2 Q2 D2 D D2 CP2 PR 2 7474 Q 2 8 3 4 CP PR 7474 Q 6 CP2 PR 2 7474 Q 2 8 CLK/6 = 62.5 Hz For 7474, pin 7=GND pin 4 = Vcc CLK CLK2 CLK4 CKL8 CLK6 f f/2 f/4 f/8 f/6 Phsx 262 Laboratory Electronics II Spring Lecture 8 Page
Ripple Down Counter CLK CLK2 CLK4 CKL8 CLK6 Q Q Q2 Q3 Hex F E D C B A 9 8 7 6 5 4 3 2 Phsx 262 Laboratory Electronics II Spring Lecture 8 Page
Ripple Up Counter CLK CLK2 CLK4 CKL8 CLK6 Q Q Q2 Q3 Hex F 2 3 4 5 6 7 8 9 A B C D E F Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 2
Astable Multivibrator The astable multivibrator is an oscillator. The period and duty cycle are properties of oscillator. t p Period f in Hertz t p t high t t t p high low t low Depending on whose definition you use thigh %Duty Cycle High t OR tlow %Duty Cycle Low t Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 3 p p
Timer Circuits - 555 Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 4
Timer Circuits - 555 Functional Block Diagram V THRES 2 V 3 CC V TRIG V 3 CC Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 5
One Shot with a 555 One shot per trigger pulse t w =.R A C (pulse width from the spec sheet) Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 6
Continuous Shots with a 555 out Low Duty Cycle <5% Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 7
Setting Frequency of a 555 clock Note: Max R A +2R B is 2M Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 8
5% Duty Cycle Clock with 555 Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 9
Display Technologies-LED LED - Light Emitting Diode Normally operates at ~ma Drops ~.7V Has typical Solid State Diode IV Characteristics Available in many different colors (Physics achievement!) +5V 33ohm Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 2
f g a 7-Segment LED Display b Connected to +5V e d MAN7A c dp 33ohm Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 2
MAN7A 7-Segment Display LED Display Devices Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 22
BCD Binary Coded Decimal maps a four bit binary code directly to decimal numbers. Great for using binary to provide the human interface, but is really inefficient binary packing so is rarely used internally in circuits. Chips are available that perform the conversion binary BCD binary. A 3 A 2 A A Dec 2 3 4 5 6 7 8 9 Undef Undef Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 23
BCD Decoder-Driver 7-Segment LED Display +5V BCD Decoder-Driver BCD Decoder -Driver 33ohm An LED is on when chip output goes low. 7-Segment LED Display Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 24
Truth Table - BCD Decoder Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 25
Lab 7: Ripple Counter with Display Q Clock 4-bit Ripple Counter Q 2 Q 3 Q 4 Sample DAC with Lab Scope8 Q 4 Q 3 Q 2 Q A 3 A 2 A A MMI a-g BCD Decoder Driver 7 segment Display Phsx 262 Laboratory Electronics II Spring Lecture 8 Page 26