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Digital Electronics Electronics Technology

Digital Electronics Electronics Technology

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Digital Electronics Electronics Technology

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  1. Digital Electronics Electronics Technology Sachin Sharma Counters

  2. ASYNCHRONOUS COUNTERS • Only LSB flip-flop controlled by the clock input • Also known as a RIPPLE COUNTER • Two or more “T” flip-flops interconnected, output • of each flip-flop connected to clock input of the next. • Modulus- number of stable states in each flip-flop cycle • Modulus = N= number of flip-flops • Highest number in count =

  3. BUILD A 4 BIT RIPPLE COUNTER 1. 4 JK flip-flops in toggle mode- all JK inputs tied high 2. Q outputs connected to clock input of following flip-flop 3. FF A = LSB (one with clock input); toggles when input clock toggles from high to low; FF D = MSB 4. FF B, C, D do not toggle till receive NGT from proceeding FF 5. Direction of count can be reversed by complementing each FF’s output or complementing each FF’s input

  4. TEST 1. What is the term for the number of counts in one counter cycle? Modulus of the counter 2. How is the modulus determined? 3. Since only the first flip-flop of a ripple counter is controlled by a clock, the counter is ____________________? Asynchronous 4. What is the mod number of a counter containing 5 flip-flops? 32 5. What is the highest count of a four bit counter? 31

  5. UNSTABLE STATE PROGRAMMING A RIPPLE COUNTER • Counters may be made to recycle after any desired count by using a gate to reset the counter. CONVERT MOD 8 TO MOD6

  6. 1. Determine smallest number of FF’s such that HOW TO BUILD A COUNTER TO GO FROM ZERO TO MOD NUMBER X 2. Connect a NAND gate output to asynchronous clears of all FF’s 3. Determine which FF’s will be high at count = X Connect the Q outputs of these FF’s to NAND gate inputs

  7. 1. Determine smallest number of FF’s such that thus 4 FF’s are required 1 1 0 0 BUILD A COUNTER THAT COUNTS FROM ZERO TO NINE (X=MOD 10) 2. Connect a NAND gate to asynchronous clears of all FF’s 3. Determine which FF’s will be high at count = X Connect the Q outputs of these FF’s to NAND gate inputs

  8. PROGRAMMING COUNTERS USING JK INPUTS • Counters can be controlled using the JK inputs • Low on JK of 1st FF will cause it to stop toggling on any count • High or low at JK inputs forces counter to skip states

  9. ASYNCHRONOUS DOWN COUNTER • Direction of count can be reversed by • (a) complementing each FF’s output or • (b) complementing each FF’s input

  10. COUNTER PROBLEM 1. What is the value of the last usable state before the NAND gate resets the circuitry? 2. What value does the NAND gate reset the value to? 3. What is the modulus of this counter? 4. If count starts at decimal 11 and receives seven clock pulses, what is the new value on the counter? 5. What is the unstable state of the counter?

  11. COUNTER PROBLEM 1. What is the value of the unstable state, in decimal? 2. At what value does the NAND gate set the counter to? 3. If QA=1, QB=1, and QC=0, and 5 clock pulses are applied: QC= QB= QA= 4. What is the modulus of this counter?

  12. BCD COUNTER • Binarycounter that counts from 0000 to 1001 before it recycles (MOD-10). • Widespread applications where pulses or events are to be counted and the results displayed on a decimal numerical read-out. • Also used for dividing a pulse frequency exactly by 10. Cascading BCD counters to count and display from 000 to 999.

  13. MOD-60 COUNTER Two 7493s can be combined to produce a MOD-60 Counter

  14. DIGITAL CLOCK

  15. COUNTERS ASYNCHRONOUS SYNCHRONOUS

  16. SYNCHRONOUS COUNTERS • Two or more FF’s connected as “T” FF’s. • All FF’s in the counter are clocked at the same time. • Advantage over the ripple counter is speed and accuracy but more complex.

  17. SYNCHRONOUS COUNTERS MOD <2 N • A NAND control gate is used to clear the counter before the full count.

  18. SYNCHRONOUS COUNTERS UP/DOWN

  19. COUNTER TYPES Asynchronous Counter (a.k.a. Ripple or Serial Counter): each FF is triggered one at a time with output of one FF serving as clock input of next FF in the chain. Synchronous Counter (a.k.a. Parallel Counter): all the FF’s in the counter are clocked at the same time. Up Counter: counter counts from zero to a maximum count. Down Counter: counter counts from a maximum count down to zero. BCD Counter: counter counts from 0000 to 1001 before it recycles. Pre-settable Counter: counter that can be preset to any starting count either synchronously or asynchronously Ring Counter: shift register in which the output of the last FF is connected back to the input of the first FF. Johnson Counter: shift register in which the inverted output of the last FF is connected to the input of the first FF.

  20. RING COUNTER Shift register counter with feedback from Q of last FF back to first FF input

  21. JOHNSON COUNTER Shift register in which the inverted output of the last FF is fed back to the input of the first FF.

  22. Lab 18. A PROGRAMMABLE COUNTER Design a four-bit counter controlled by two control lines X and Y that behaves according to the truth table.

  23. Lab 18. A PROGRAMMABLE COUNTER

  24. RIPPLE COUNTER Binary Output Clock Input 1 0 0 0 0 1 1 1 0 1 1 0 0 0 1 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 1 0 1 0 0 Pulse 5 Pulse 8 Pulse 7 Pulse 6 Pulse 4 Pulse 1 Pulse 2 Pulse 3 This 4-bit counter has 16 states and will count from binary 0000 through 1111 and then reset back to 0000. The counter has amodulus of 16. On the next clock pulse (8) all FFs will toggle because each will receive aH-to-Lpulse- one after another. Watch the count ripple thru the counter. PS and CLR input are INACTIVE All J-K flip-flops in the TOGGLE MODE

  25. Clock input 1s output 2s output 4s output RIPPLE COUNTER WITH WAVEFORMS Binary Output Clock Input 0 0 1 1 0 1 0 0 0 0 0 1 0 1 0 1 0 0 1 0 0 0 0 0 Pulse 5 Pulse 1 Pulse 2 Pulse 3 Pulse 4 FFs triggered on H-to-L pulse. CLK toggles 1s FF. 1s FF toggles 2s FF. 2s FF toggles 4s FF.

  26. Short negative pulse To clear input of each FF DECADE COUNTER Initial count at 0111 Binary Output Clock Input 1 0 0 1 0 0 0 0 0 0 0 1 0 0 1 0 0 1 1 1 0 1 0 0 0 1 0 1 1 0 0 0 0 0 1 1 Pulse 7 Pulse 6 Pulse 5 Pulse 4 Pulse 3 Pulse 2 Pulse 1 Pulse 8 All J & K inputs = 1 All PR inputs = 1 Count is at 1001. Next clock pulse will increment counter for a short time to 1010 which will activate the NAND gate and reset the counter to 0000. To change mod-16 counter to decade counter: Reset count to 0000 after 1001 (9) count. When count hits 1010 reset to 0000. See added 2-input NAND gate that clears all JK FFs to 0 when count hits 1010.

  27. DOWN COUNTER Initial count set at binary 111 1 1 1 1 1 0 1 0 1 1 0 0 0 1 1 0 1 0 Pulse 4 Pulse 2 Pulse 1 Pulse 3 Pulse 5 Changes from Ripple Up Counter are wiring from Q’ outputs (instead of Q outputs) to the CLK input of the next FF.

  28. SELF-STOPPING DOWN COUNTER Watch count on Pulse 8. The count remained at binary 000. 1 1 0 1 0 0 1 0 1 1 1 1 0 0 1 0 0 0 0 1 0 0 1 1 Pulse 2 Pulse 4 Pulse 3 Pulse 1 Pulse 5 Pulse 6 Pulse 8 Pulse 7 This is a 3-bit down counter. The 1s FF is in TOGGLE mode when counting (J & K = 1). The 1s FF switches to HOLD mode when the J and K inputs are forced LOW by the OR gate when the count decrements to 000. The count stops at 000.

  29. 200 Hz Clock Input 400 Hz 100 Hz 50 Hz COUNTER USED FOR FREQUENCY DIVISION  4  8  2  16 800 Hz

  30. ? Hz 400 Hz ? Hz ? Hz 100 Hz 800 Hz USING THE 7493 COUNTER IC • Counters are available in IC form. • Either ripple (7493 IC) or synchronous (74192 IC) counters are available. 1600 Hz 7493 Counter IC wired as a 4-bit binary counter

  31. A(0) A(1) 74HC85 Magnitude Comparator A(2) A(3) A > B B(0) A = B B(1) A < B B(2) B(3) MAGNITUDE COMPARATOR A magnitude comparator is a combinational logic device that compares the value of two binary numbers and responds with one of three outputs (A=B or A>B or A<B). Input binary 0111 Input binary 1111 Input binary 0001 HIGH HIGH Input binary 0111 Input binary 0110 Input binary 1100 HIGH

  32. TROUBLESHOOTING EQUIPMENT • Logic Probe • Logic Pulser • Logic Clip (logic monitor) • Digital IC Tester • DMM/Logic Probe • DMM or VOM • Dual-trace Oscilloscope • Logic Analyzer

  33. SIMPLE TROUBLESHOOTING HINTS • Feeltop of IC to determine if it is hot • Lookfor broken connections, signs of excessive heat • Smellfor overheating • Checkpower source • Tracepath of logic through circuit • Knowthe normal operation of the circuit