MSI Counters

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MSI Counters

  1. 1. MSI Counter• 4-bit synchronous counter – edge-triggered – synchronously presettable – cascadable• Typical Count Rate of 35 MHz• ‘160 and ‘162, Mod-10• ‘161 and ‘163, Mod-16 1
  2. 2. MSI Counter• 74LS163 4-bit synchronous counter 16-pin DIP 2
  3. 3. MSI Counter• 74LS163 characteristics – edge-triggered – synchronously presettable – cascadable – count modulo 16 (binary) 74x163• Synchronous Reset (Clear) input that overrides all other control inputs – active only during the rising clock edge 3
  4. 4. MSI Counter• 74LS163 logic symbols datasheet text 74x163 4
  5. 5. MSI Counter• 74LS163 state diagram and logic equations 5
  6. 6. MSI Counter• 74LS163 mode select table• All signals must be high ( H ) to enable the count sequence to begin 6
  7. 7. MSI Counter• 74x163 is a synchronous 4-bit binary counter• RCO=1 when all count bits are 1 and ENT is asserted 7
  8. 8. MSI Counter • The control inputs for the 74x163 have the following effects:clear load holdhold 8
  9. 9. 74x163Internal Logic Diagram
  10. 10. Counter Operation• Free-running ÷16• Count if ENP and ENT both asserted• Load if LD is asserted (overrides counting)• Clear if CLR is asserted (overrides loading and counting)• All operations take place on rising CLK edge makes it free-running• RCO is asserted if ENT is asserted and Count = 15 10
  11. 11. Free-Running 4-Bit ’163 Counter• “divide-by-16” counter• RCO is asserted if ENT is asserted and Count = 15 11
  12. 12. Modified Counting Sequence DCBA• Load 0101 (5) after Count = 15• 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 5, 6, …• “divide-by-11” counter 12
  13. 13. Another Way• Clear after Count = 1010 (10)• 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0, 1, 2, 3, …• “modulo-11” or “divide-by-11” counter 13
  14. 14. Countingfrom 3 to 12 14
  15. 15. Cascading Counters• For modulus greater than 16• RCO (ripple carry out) is asserted in state 15, if ENT is asserted 15
  16. 16. Decoding Binary-Counter States• A binary counter may be combined with a decoder to obtain a set of 1-out-of-m coded signals, where one signal is asserted in each counter state Useful when counter outputs are used to control a set of devices A different device is enabled in each counter state In this approach each output of the decoder enables a different device The next slide shows the 74163 wired as a modulo 8 counter combined with a 74138 (3 to 8 decoder) The decoder output provides eight signals, each one representing a counter state 16
  17. 17. Decoding Binary-Counter States 17
  18. 18. Decoding Binary-Counter States• The next slide shows a typical timing diagram for this circuit• Each decoder output is asserted during a corresponding clock period• The decoder outputs may contain “glitches” on state transitions where two or more counter bits change• This happens even though the 74163 outputs are glitch free and the 74138 does not have any static hazards• In a synchronous counter like the 74163 the outputs don’t change exactly at the same time• Moreover multiple signal paths in a decoder like 74138 have different delays; thus the output may have glitches• This problem is an example of functional hazard 18
  19. 19. Decoder Waveforms• Glitches may or may not be a concern 19
  20. 20. Glitch-Free Outputs• In most applications these would be used as control inputs to counters, registers and other edge triggered devices• In such a case there is no problem as the glitches occur after the clock tick• They would be a problem if applied to latches• They would also be a problem if utilized as a clock• One way to “clean-up” these glitches is to connect the 74138 decoder output to another register• This register would sample the stable decoded outputs on the next clock tick as shown in the next slide• In this case the final outputs would have to be renamed to account for the one clock tick delay through the register 20
  21. 21. Glitch-Free Outputs• Register outputs delayed by one clock cycle 21
  22. 22. 74161 MSI Counter• The 74163 is fully synchronous• Some applications require an asynchronous clear function• That is provided by 74161• It has the same pinout as 74163• Its CLR_L input is connected to the asynchronous clear inputs of its flip flops
  23. 23. Modulo-10 Counters• From the 74LS163 “family” – the 74LS160 – 74LS160 in free-running mode – Duty cycle of QC and QD is not 50% 23
  24. 24. Modulo-10 Counters• 74LS160 state diagram• The 74LS160 (and 74LS162) can be preset to any state, but will not count beyond 9.• If preset to state 10, 11, 12, 13, 14, or 15, it will return to its normal sequence within two clock pulses.• 74160 has asynchronous clear as in 74161 24
  25. 25. Up/Down Counters• A 3-bit binary up/down counter (block diagram) QA Clock QB Counter Count QC UP / DOWN 25
  26. 26. Up/Down Counters• A 3-bit binary up/down counter (State diagram) 26
  27. 27. Up/Down Counters 27
  28. 28. Up/Down Counters• This circuit is a 3-bit UP/DOWN synchronous counter using JK flip-flops configured to operate as toggle or T-type flip- flops giving a count of zero (000) to seven (111) and back to zero again.• An additional input determines the direction of the count, either UP or DOWN and the timing diagram gives an example of the counters operation as this UP/DOWN input changes state. 28
  29. 29. Timing diagram
  30. 30. Up/Down Counters• The 74LS169 is a fully synchronous 4-stage up/down counter• Includes: – a preset capability for programmable operation – carry lookahead for easy cascading – a U/ D input to control the direction of counting 30
  31. 31. Up/Down Counters• The SN74LS169 operates in a Modulo-16 binary sequence 31
  32. 32. 74LS169 logic circuit diagram
  33. 33. Up/Down Counters• 74LS169 logic symbol • Functions similar to 74163 • Difference is that its carry output and enable inputs are active low • It is an up/down counter • It counts ascending or descending binary order depending on the value of input signal UP/DN • Counts up when UP/DN is 1 • Counts down when UP/DN is 0 33
  34. 34. MSI Counters• 7458: Dual 4-bit Decade Counter • 74454: Dual Decade Up/Down Counter, Synchronous, Preset Input• 7459: Dual 4-bit Binary Counter • 74455: Dual Binary Up/Down Counter, Synchronous, Preset Input• 7468: Dual 4 Bit Decade or Binary Counters • 74461: 8-bit Presettable Binary Counter with three-state outputs• 7469: Dual 4 Bit Decade or Binary Counters • 74490: Dual Decade Counter• 7490: Decade Counter (separate Divide-by-2 and Divide-by-5 sections) • 74491: 10-bit Binary Up/Down Counter with Limited Preset and three-state• 7492: Divide-by-12 Counter (separate Divide-by-2 and Divide-by-6 logic outputs sections) • 74560: 4-bit Decade Counter with three-state outputs• 7493: 4-bit Binary Counter (separate Divide-by-2 and Divide-by-8 sections) • 74561: 4-bit Binary Counter with three-state outputs• 74142: Decade Counter/Latch/Decoder/Nixie Tube Driver • 74568: Decade Up/Down Counter with three-state outputs• 74143: Decade Counter/Latch/Decoder/7-segment Driver, 15 mA Constant • 74569: Binary Up/Down Counter with three-state outputs Current • 74590: 8-Bit Binary Counter with Output Registers and three-state outputs• 74144: Decade Counter/Latch/Decoder/7-segment Driver, 15V open • 74592: 8-Bit Binary Counter with Input Registers collector outputs • 74593: 8-Bit Binary Counter with Input Registers and three-state outputs• 74160: Synchronous 4-bit Decade Counter with Asynchronous Clear • 74668: Synchronous 4-bit Decade Up/Down Counter• 74161: Synchronous 4-bit Binary Counter with Asynchronous Clear • 74669: Synchronous 4-bit Binary Up/Down Counter• 74162: Synchronous 4-bit Decade Counter with Synchronous Clear • 74690: 4-bit Decimal Counter/Latch/Multiplexer with Asynchronous Reset,• 74163: Synchronous 4-bit Binary Counter with Synchronous Clear Three-State Outputs• 74168: Synchronous 4-Bit Up/Down Decade Counter • 74691: 4-bit Binary Counter/Latch/Multiplexer with Asynchronous Reset,• 74169: Synchronous 4-Bit Up/Down Binary Counter Three-State Outputs• 74176: Presettable Decade (Bi-Quinary) Counter/Latch • 74692: 4-bit Decimal Counter/Latch/Multiplexer with Synchronous Reset,• 74177: Presettable Binary Counter/Latch Three-State Outputs• 74190: Synchronous Up/Down Decade Counter • 74693: 4-bit Binary Counter/Latch/Multiplexer with Synchronous Reset,• 74191: Synchronous Up/Down Binary Counter Three-State Outputs • 74694: 4-bit Decimal Counter/Latch/Multiplexer with Synchronous and• 74192: Synchronous Up/Down Decade Counter with Clear Asynchronous Resets, three-state outputs• 74193: Synchronous Up/Down Binary Counter with Clear • 74695: 4-bit Binary Counter/Latch/Multiplexer with Synchronous and• 74196: Presettable Decade Counter/Latch Asynchronous Resets, three-state outputs• 74197: Presettable Binary Counter/Latch • 74696: 4-bit Decimal Counter/Register/Multiplexer with Asynchronous• 74290: Decade Counter (separate divide-by-2 and divide-by-5 sections) Reset, three-state outputs• 74291: 4-bit Universal Shift register, Binary Up/Down Counter, • 74697: 4-bit Binary Counter/Register/Multiplexer with Asynchronous Synchronous Reset, three-state outputs• 74293: 4-bit Binary Counter (separate divide-by-2 and divide-by-8 • 74698: 4-bit Decimal Counter/Register/Multiplexer with Synchronous sections) Reset, three-state outputs• 74390: Dual 4-bit Decade Counter • 74699: 4-bit Binary Counter/Register/Multiplexer with Synchronous Reset,• 74393: Dual 4-bit Binary Counter three-state outputs• 74452: Dual Decade Counter, Synchronous • 74716: Programmable Decade Counter• 74453: Dual Binary Counter, Synchronous • 74718: Programmable Binary Counter 34
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