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Chap. 7 Counters and Registers

Chap. 7 Counters and Registers. Introduction Chap. 7 의 내용 How FFs and logic gates can be combined to produce different types of counters and registers Divided into 2 parts Part I : principles of counter operation, various counter circuit arrangement, and

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Chap. 7 Counters and Registers

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  1. Chap. 7 Counters and Registers • Introduction • Chap. 7의 내용 • How FFs and logic gates can be combined to produce different types of counters and registers • Divided into 2 parts • Part I : principles of counter operation, various counter circuit arrangement, and representative IC counters • Part II : counter application, types of IC register, and troubleshooting • 7-1 Asynchronous(Ripple) Counters • Asynchronous Counter : Fig. 7-1 • The FFs do not change states in exact synchronism with the applied clock pulses • Ripple Counter • The FFs respond one after another in a kind of rippling effect • The terms asynchronous counter and ripple counter interchangeably • Signal Flow(in Fig. 7-1) • Left-to-Right : Conventional signal flow • Right-to Left : • FF A(rightmost) = LSB, FF D(leftmost) = MSB We’ll break left-to-right convention, especially in counter diagrams

  2. Exam. 7-1)Some time later the clock pulses are removed, and the counter FFs read 0011. How many clock pulses have occurred? • 3 + 16 = 19 + 16 = 35 + 16 = 51 ….. • Mod Number = 2N( N : number of FF ) • Number of different states • Fig. 7-1 : MOD-16 ripple counter ( 0000  1111) • Exam. 7-2)The counter must be able to count as many as one thousand items. How many FFs are required ? • 10 FFs : 0  1023 ( 1001  1023은 필요 없음 ) • Frequency Division • For any counter, the output from the last FF(the MSB) divides the input clock frequency by the MOD number of the counter • MOD-16 Counter = Divide-by-16 Counter : Fig. 7-2 • Exam. 7-3)How many FFs are required for the MOD-60 counter? • There is no integer power of 2 that will equal 60 : 26 = 64 • In the next section we will see how to modify the basic counter so that any MOD number can be obtained.

  3. 7-2 Counters with MOD Number < 2N • Mode Number less than 2N: • The basic counter can be modified to produce MOD numbers less than 2N by allowing the counter to skip states • MOD-6 Counter : Fig. 7-4 • When B = C = “1”, NAND output will go “0” (few nanosecond spike or glitch) • This glitch is very narrow and so would not produce any visible indication on LEDs • However It could cause a problem if the B output were being used to drive other circuitry • State Transition Diagram : Fig. 7-5 • Dotted line : Temporary state(=110) • 111 state : never reached, not even temporarily • Displaying Counter States • Output A = “1” : Inverter output = “0” LED ON • Output A = “0” : Inverter output = “1” LED OFF • Exam. 7-4) a) LED status of 5, b) LED clocked by 1 kHz, c) LED will be visible for 110 in Fig.7-5 • Exam. 7-5) Determine the MOD number and the frequency at the D output of the counter in Fig.7-6(a) • D C B A = 1 1 1 0 = 14 일 때 NAND output = 0 (Clear Input) : MOD 14 • 30 kHz/14 = 2.14 kHz

  4. General Procedure (to construct MOD X Counter) • 1) Find the smallest number of FFs such that 2N  X, connect them as a counter. If 2N = X, do not do steps 2 and 3 • 2) Connect a NAND output to the CLEAR inputs of all the FFs • 3) Determine which FFs will be in the HIGH state at a count = X; then connect the outputs of these FFs to the NAND inputs. • Exam. 7-6)Construct a MOD-10 (count from 0000 ~ 1001) counter : Fig. 7-6(b) • Find the smallest number of FFs : 4 ( 24 = 16 ) • D C B A = 1 0 1 0 = 10 : D and B must be connected as the NAND gate input • Decade Counters/BCD counters : Fig. 7-6(b) or 별도 IC • MOD-10 Counter = Decade Counter = BCD Counter • Count in sequence from 0000(0) to 1001(9) • Exam. 7-7)Construct a MOD-60 Counter : Fig. 7-7 • Find the smallest number of FFs :64 ( 26 = 64 ) • Q5 Q4 Q3 Q2 Q1 Q0 = 1 1 1 1 0 0 = 60 (32 + 16 + 8 + 4)

  5. 7-3 IC Asynchronous Counters • 74LS293 Asynchronous Counter IC : Fig. 7-8 • Q0와 CP1이 연결되지 않은 이유 : 3 or 4 비트 카운터로 사용 가능 • Exam. 7-8)How the 74LS293 should be connected to operate as a MOD-16 counter : Fig. 7-9 • MR1 = MR2 = “0”, CP1 = Q0, Q3 = 10 kHz/16 = 625 Hz • Exam. 7-9)How to wire the 74LS293 as a MOD-10 Counter : Fig. 7-10 • Q3 Q2 Q1 Q0 = 1 0 1 0 = 10 (8 + 2) • Exam. 7-10)How to wire the 74LS293 as a MOD-14 Counter : Fig. 7-11 • Q3 Q2 Q1 Q0 = 1 1 1 0 = 14 (8 + 4 + 2) • Exam. 7-11)Construct a MOD-60 Counter with 74LS293 : Fig. 7-12 • MOD-10 counter X MOD-6 counter = MOD-60 counter • MOD-10 counter : Exam. 7-9 • MOD-6 counter : Q0는 사용하지 않고 3 비트(Q3 Q2 Q1)만 사용 MR1 MR2 Clear ( C0 )

  6. CMOS Asynchronous Counters • 74HC4024 : MOD-128 ripple counter = CTR DIV128 ( Fig. 7-14 ) • 74HC4040 : MOD-4096 ripple counter • 7-4 Asynchronous Down Counter • MOD-8 Down Counter : Fig. 7-15 • The inverted output of each FF is connected to the CLK input of following FF. • 7-5 Propagation Delay in Ripple Counters • Ripple Counter • The simplest type of binary counter • Decoding Glitch : Sec. 7-12 • Propagation Delay : Fig. 7-16 • The Nth FF cannot change states until a time Nxtpd after the clock transition occurs. • For proper counter operation • Tclock  N x tpd fmax = 1 /( N x tpd ) • Exam) 74LS112, tpd = tPHL = 24 ns • 4 FFs : fmax = 1 / 4 x 24 ns = 10.4 MHz • 6 FFs : fmax = 1 / 6 x 24 ns = 6.9 MHz * FF 개수 증가 The total propagation delay 증가하고 fmax 감소

  7. 7-6 Synchronous(Parallel) Counter • Synchronous/Parallel Counters • All of the FFs are triggered simultaneously (in parallel) by the clock input pulses • Synchronous MOD-16 Counter : Fig. 7-17 • Circuit Operation • Each FF should have its J and K inputs connected such that they are HIGH only when the outputs of all lower-order FFs are in the HIGH state • Advantage of Synchronous Counters over Asynchronous • Total Delay in Synchronous Counter • Total Delay = Single FF tpd + Single AND gate tpd • Total delay is the same no matter how many FFs are in the counter • Actual ICs • 74LS160/162, 74HC160/162 : Synchronous Decade(MOD-10) Counters • 74LS161/163, 74HC161/163 : Synchronous MOD-16 Counters • Exam. 7-12) (a) Determine fmax for the counter of Fig. 7-17(a) and Compare this value with MOD-16 ripple counter( FFtpd = 50 ns, AND gate tpd = 20 ns) • Parallel Counter : fmax = 1 / ( 50 ns + 20 ns ) = 14.3 MHz • Ripple Counter : fmax = 1 / (4 x 50 ns ) = 5 MHz A B C ABC = (J = K) Design in 7-14 p. 362 A B AB =( J = K)

  8. (b) What must be done to convert this counter to MOD-32 • 5 개째 FF(25 = 32) 이 추가되며, J and K input are fed by the output of a four input AND gate whose inputs are A, B, C, and D (c) Determine fmax for the MOD-32 parallel counter • FF 개수에 관계없이 14.3 MHz • 7-7 Synchronous Down and Up/Down Counters • MOD-8 Parallel Up/Down Counter : Fig. 7-18 • Up Count : Up/Down = 1, AND gates 1/2 = Enabled, AND gates 3/4 = Disabled • Down Count : Up/Down = 0, AND gates 1/2 = Disabled, AND gates 3/4 = Enabled • Exam. 7-13)What problems might be caused if the Up/Down signal changes levels on the NGT of the clock ? • Possible Problems : Unpredictable results of FF • the J and K inputs change at about the same time that a NGT occurs at their CLK input. • Effects : Predictable results of FF(No problems) • the effects of the change in the control signal must propagate through two gates before reaching the J, K inputs(결국 다음 Clock에서 Up/Down 동작이 가능함)

  9. 7-8 Presettable Counters • Presettable Counter/Parallel Loading Counter • Preset to any desired starting count either asynchronously or synchronously • Presettable Parallel Counter with Asynchronous Preset : Fig. 7-19 • The counter is loaded with any desired count at any time • 1) Apply the desired count to the parallel data inputs, P2, P1, and P0 • 2) Apply a Low pulse to the PARALLEL LOAD input(PL) • PL 은 Active Low이고, 이 때 2 개 NAND Gate의 한 개 입력은 항상 1, 따라서 P에 의해 P = 1 이면 PRESET, 그리고 P = 0 이면 CLR • Asynchronous Presetting IC Counters • TTL : 74LS190, 191, 192, 193 • CMOS : 74HC190, 191, 192, 193 • Synchronous Presetting • The counter is preset on the active transition of the same clock signal • Synchronous Presetting IC Counters • TTL : 74LS160, 161, 162, 163 • CMOS : 74HC160, 161, 162, 163 Async presetting에서는 PRE/CLR에 의해

  10. 7-9 The 74LS193/HC193 • Presettable Up/Down Counter(74LS193) : Fig. 7-20 • Synchronous Counter, Asynchronous Preset, and Asynchronous Master Reset • Terminal Count : Fig. 7-21 • TCU : 1111 0000 ( Fig. 7-22에서 t6, t7참고 ) • TCD : 0000 1111 ( Fig. 7-23에서 t9, t10참고 ) • Exam. 7-14)Determine the counter output waveforms in Fig. 7-22(a) • Up Counter : Fig. 7-22(b) • Exam. 7-15)Determine the counter output waveforms in Fig. 7-23(a) • Down Counter : Fig. 7-23(b) • Variable MOD Number Using the 74LS193 • TCD = PL : Preset to 0101(5) - Fig. 7-24 • Q2 = 5 Clock cycle : Divide the frequency by 5 • MOD-6 가 아니고 MOD-5 인 이유 • the counter gets preset back to 5 in the middle of a clock cycle • We can vary the frequency division by changing the logic levels applied to the parallel data inputs • A variable frequency-divider can be easily implemented by connecting switches to the parallel data inputs in Fig. 7-24 5, 4, 3, 2, 1, 0, 5, 4, 3, 2, 1, ...

  11. Multistage Arrangement : Fig. 7-25 • 8 bits Up/Down Counter using two 74LS193s • 7-11 Decoding a Counter • Decoding • Electronically decode the contents of a counter and display the results • Immediately recognizable and require no mental operations • Active-HIGH Decoding : Fig. 7-27 • At any one time only one AND gate output is HIGH • Exam. 7-16)How many AND gates are required to decode all of the states of a MOD-32 counter? What are the inputs to the gate that decodes for 21 • MOD-32 counter has 32 possible states : 32 개 AND gate 필요 • 1 0 1 0 1(21) : E, D, C, B, A • Active-LOW Decoding • NAND gates are used in place of AND gates • Exam. 7-17)Generate a control waveform which could be used to control devices such as a motor, solenoid valve, or heater. • Control Signal Generation(On/Off control) : Fig. 7-28 • The X output is HIGH between the counts of 8 and 14 for each cycle of counter

  12. BCD Counter Decoding • Decoder/Display Unit : Fig. 7-29 (refer to p. 512) • 7-12 Decoding Glitches • Decoding Glitches : Fig. 7-30 • The propagation delays between FF transitions cause problems when decoding a ripple counter • Decoder X0 = Temporary 00 state 에서 Glitch 발생 : A = B = 0 (X0=1) • Strobing : Fig. 7-31 • A reliable method for eliminating the decoder glitches : Strobe Signal • Decode AND gates disabled until all of the FFs have reached a stable state • 7-13 Cascading BCD Counters • Cascading BCD Counters : Fig. 7-32 • Count and Display numbers from 000 to 999 • 2 가지 Implementation • 1) 74LS293 wired as a MOD-10 counter • 2) 74LS90 또는 74LS192/HC192 BCD IC counter

  13. 7-14 Synchronous Counter Design • Design a 3 bits Counter • 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, … (Undesired State : 5, 6, 7) : Tab. 7-3 • Design Procedure • 1) Determine the desired number of bits(FFs) and the desired counting sequence • FFs = 3 개, Desired Sequence = 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, …. • 2) Draw the state transition diagram : Fig. 7-33 • 3) Tabulate present/next state table : Tab. 7-4 • Use the state transition diagram to setup a present/next state table • 4) Tabulate circuit excitation table : Tab. 7-5 • Add a column to this table for each J and K input by using Tab. 7-2

  14. 5) Design logic circuits to generate the levels required at each J and K input • FF A : Fig. 7-34 • FF B : Fig. 7-35(b) • FF C : Fig. 7-35(a) • 6) Implement the final expressions : Fig. 7-36 • Stepper Motor Control • Step Motor Drive Circuit(with Direction Control) : Fig. 7-37(a) • State Transition Diagram : Fig. 7-37(b) • Circuit Excitation Table : Tab. 7-6 • K-map Simplification : Fig. 7-38 • Implementation : Fig. 7-39 • 7-15 Shift-Register Counters • Shift-Register • Transfer data left to right, or vice versa, one bit at a time(serially) • Shift-register counters use feedback • the output of the last FF in the register is connected back to the first FF in some way • Ring Counter • In most instances only a single 1 is in the register

  15. MOD-4 Ring Counter : Fig. 7-40 • Ring counters can be constructed for any desired MOD number • A MOD-N ring counter used N flip-flops • Starting a Ring Counter • A ring counter must start off with only one FF in the 1 state and all the others in the 0 state • Ring Counter Starter : Fig. 7-41 • 1) On power-up, the capacitor will charge up relatively slowly toward Vcc, 따라서 Inverter 1 input = 0 • 2) Inverter 1 output = 1, 따라서 Inverter 2 output = 0 until Inverter 1 input = 1 • 이때 Q3 = PRE, Q2 = Q1 = Q0 = CLR 임으로 1 0 0 0 으로 Preset 됨 • Johnson Counter/Twisted Ring Counter • The inverted output of the last FF is connected to the input of the first FF • 3 bits Johnson counter : Fig. 7-42 • MOD-6(six distinct states) : 000, 100, 110, 111, 011, and 001 • 50 percent duty cycle square wave at one-sixth the frequency of the clock • MOD-N counter(N= even number) by connecting N/2 FFs • MOD-10 Johnson Counter : 5 FF 필요 4 distinct states

  16. Decoding a Johnson Counter • For a given MOD number, a Johnson counter requires only half the number of FFs that a ring counter requires • MOD-8 Ring Counter : 8 FFs • MOD-8 Johnson Counter : 4 FFs • Ring Counter does not require decoding gates • only one FF in the 1 state and all the others in the 0 state : Fig. 7-40(c) Sequence Table • Johnson Counter requires decoding gates : Fig. 7-43 • Each decoding gate has only two inputs, even though there are three FFs in the counter • Two of the three FFs are in a unique combination of states • IC Shift-Register Counters • Ring/Johnson Counter는 너무 간단하게 구현 됨으로 IC가 별로 없다 • CMOS Johnson-Counter : 74HC4017, 74HC4022

  17. 7-16 Counter Applications : Frequency Counter • Frequency Counter : Fig. 7-44 • Counter + Decoder/Display + AND gate • Sampling Interval : SAMPLE pulse goes HIGH from t1 to t2 • During this sampling interval the unknown frequency pulses(fx) will pass through the AND gate and will be counted by the counter • The accuracy of this method depends almost entirely on the duration of the sampling interval • The sampling Interval must be very accurately controlled • Exam. 7-18)The unknown frequency is 3792 pulses per second(pps). Determine the counter reading after a sampling interval of (a) 1 s, (b) 0.1 s, and (c)10ms • (a) 1 s : 3792 (b) 0.1 s : 379.2, 379 or 380 (c) 0.01 s : 37.92, 37 or 38 • A method for obtaining accurate sampling interval : Fig. 7-45 • Crystal Oscillator : generate a very accurate 100-kHz waveform • Decade Counter : divide 100-kHz frequency by 10 • Rotary Switch : select one of the decade-counter output • Flip-Flop : 2 분주 • In position 1 : 1 Hz / 2 = 0.5 Hz • Q = 0.5 Hz = 1 / 0.5 Hz = 2 T, 따라서 HIGH 상태의 반주기는T (Sampling Interval)

  18. Exam. 7-19)The unknown input frequency is between 1, 000 pps and 9,990 pps, what is the best setting for the switch position in Fig. 7-45 with 3 BCD counter and display. • With three BCD counter : total capacity = 000 - 999 • 0.1 s sampling interval : 100 - 999 • Complete Frequency Counter : Fig. 7-46 • X : FF의 출력(= One-shot 의 Clock input) • SAMPLE pulse의 2 분주이고 100ns One-shot pulse를 Trigger 시켜 Counter를 Clear 함. • AND gate에 의해 SAMPLE pulse와 X 가 모두 HIGH 일 때만 Counter 동작 • 예제) Sampling Interval = 1 s, 그리고 unknown frequency = 237 pps 인 경우 • t1 - t2 : X = 0으로 동작하지 않음 • t2 - t3 : Counter is cleared to 0 and display 0 for 1 s ( = sample interval = 1 s ) • t3 - t4 : Counter는 1 s 동안 0 - 237 까지 Count • t4 - t6 : 2 s 동안 237 Display • 7-17 Counter Application : Digital Clock • Digital Clock operating from 60 Hz : Fig. 7-47 • Schmitt-trigger circuit : produce square pulses at the rate of 60 pps • MOD-60 Counter : divide the 60 pps down to 1 pps

  19. Detailed Hour Section : Fig. 7-48 • MOD-2 ( 0 -1 ) + MOD-10 ( 0 - 9 ) Counter • MOD-10 Counter : 74LS192(Presettable BCD Counter) • MOD-2 Counter : JK Flip-Flop • 12 에서 13 이 될 때 74LS192의 PL에 의해 상위 시간 = 0 (74LS112는 Clear), 그리고하위 시간 = 1( P3 P2 P1 P0 = 0 0 0 1)이 된다. • 3 Input NAND gate 에서 상위 시간 X = 1, 그리고 하위 시간 Q1 Q0 = 11(3) 일 때 PL Enabled • Q3 = 1, 즉 하위 시간 = 9 일 때 상위 시간 = 1 이 된다( 09 10). • 7-18 IC Registers • 1) Parallel in/Parallel out : 74174, 74178 • 2) Serial in/Serial out : 4731B • 3) Parallel in/Serial out : 74165 • 4) Serial in/Parallel out : 74164 • 7-19 Parallel in/Parallel out : 74174 and 74178 • 74174 and 74HC174( 6 bit register ) : Fig. 7-49

  20. Exam. 7-20A)How to connect 74ALS174 so that D5  D4  D3  D2  D1  D0 ( = data input at D5 and data output at Q0 ). • Fig. 7-50 • Exam. 7-20B)How to connect two 74ALS174 to operate as a 12 bit shift register. • Connect the Q0 of the first IC to the D5 of the second IC. • 7-20 Serial in/Serial out : 4731B • 4731B(CMOS Quad 64-bit) : Fig. 7-51 • 64 개 D-type Flip-Flop : 4 개가 one chip 이므로 총 256 개 FF • Buffer circuit : Q63 (triangle symbol with no inversion bubble) • A buffer does not change the signal’s logic level • It is used to provide a greater output-current capability than normal

  21. Exam. 7-21)Delay circuit using 4731B chip : Fig. 7-52 • Q63 goes HIGH approximately 64 clock cycles after Ds input • 7-21 Parallel in/Serial out : 74165, 74LS165, and 74HC165 • 8-bit parallel in/serial out register : Fig. 7-53 • Truth Table • Exam. 7-22)Determine (a)the conditions necessary to load the register with parallel data, (b) the conditions necessary for the shifting operation • (a) SH/LD = 0 : only Q7 will be externally available • (b) SH/LD = 1, CP INH = 0, and PGT Clock Pulse at CP • Exam. 7-23)What signal will appear at Q7(Q7=Ds, CP=200kHz, CP INH=0) • 8-bit Johnson counter divided by 16 = 12.5 kHz

  22. 7-22 Serial in/Parallel out : 74164, 74LS164, and 74HC164 • 8-bit serial in/parallel out shift register : Fig. 7-54 • Each FF output externally accessible : Q0, Q1, …, Q7 • 2 input AND gate : one input can be used for control • Exam. 7-24)Determine the sequence of states in Fig. 7-55(a) (Initial Content of the 74ALS164 = 00000000) • The correct sequence : Fig. 7-57(b) • Q7 =1 : Temporary state • LOW at MR ( inverted Q7 ) resets the register back to 00000000 • Other Register ICs • 74194/LS194/HC194 : 4 bit bi-directional universal shift register • 4 mode : shift left, shift right, parallel in, parallel out ( selected by 2 bit mode select code as inputs ) • 74373/LS373/HC373 : 8 bit parallel in/parallel out register • 8 D latch with tri-state outputs : Data or Address bus buffer로 주로 사용됨 • Pin 11 : Latch Enable(LE)로 Level trigger = 1 일 때 8 개 입력 D0 - D7 이 8개 출력 Q0 - Q7으로 출력됨(따라서 Transparent Latch 라고도 함) • 74374/LS374/HC374 : 8 bit parallel in/parallel out register • 8 edge-triggered D Flip-Flops with tri-state outputs • Pin 11 : Clock Pulse(CP)로 Edge trigger(PGT) 일 때 373과 마찬가지로 출력됨

  23. 7-24 Trouble Shooting • Exam. 7-25)Determine the possible faults of MOD-10 counter in Fig. 7-57(a) ( The displayed waveforms of the Q output with an oscilloscope are shown in Fig. 7-57(b) ) • 이상 증상 : Q1, Q2, and Q3(except Q0) are stuck in the LOW state • 이상 가능성 : • 1) Q1 : internally or externally shorted to ground • 2) MR1 : internally shorted to ground (Q1=0) • 3) Q0 와 CP1 사이의 Open : 따라서 Q1 이 Clock Input을 받지 못함 • 4) IC 자체의 internal fault • Exam. 7-26)위의 4 가지 이상 가능성을 조사했으나 모두 아니었으며, Fig. 7-58 과 같이 Q1에서 glitch를 발견했음. 이상 원인은 ? • MR2 의 Open : MR2 = HIGH in TTL • Q1의 glitch에 의해 항상 0 으로 reset 됨, 따라서 MOD-2 카운터로 동작했음( 0, 1 ) • Exam. 7-27)The displayed frequency is exactly twice in Fig. 7-46, What is the probable cause for the malfunction ? • 3 input AND gate 의 가운데 입력이 Open 되었음 : SAMPLE pulse = HIGH: • 따라서 t3 와 t4 동안만 sampling 되지 않고, t2 와 t4 동안 sampling 되었음. • Exam. 7-28)The HOURS section displays in the manner shown in Tab. 7-7 . 이상 원인은 ? (p. 382, Fig. 7-48참고 ) • 74LS192의 Q3이 아니고 Q2 가 74LS112의 CLK에 잘못 연결됨 • 따라서 9 0 일 때 X = 1로 되야 하나, 7 8 일 때 X = 1로 되었음. p. 333, Fig. 7-12 참고

  24. 7-25. Programming PLDs as Counter Circuits using Boolean Equations • General Architecture of GAL PLD • .D extension : F/F output is connected to the PLD output pin. • Q4.D = F/F Q4의 입력 =Q4의 next state • Exam. 7-29Design 3-bit MOD 6 Johnson Counter using GAL 16v8 (p. 373, Fig. 7-42참고 ) • Present-Next State Table : Tab. 7-8 • Q2.D = 000 or 100 or 110; Q1.D = 100 or 110 or 111; Q0.D = 110 or 111 or 011; • Another Method : field name twisted • D input should be 100(4) if the present state of twisted 000(0) OR………… • CUPL file : Fig. 7-60

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