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ECE-135 REGISTERS AND COUNTERSMOHINDER BASSI
CS1104-13Lecture 13: Sequential Logic: Counters and Registers2Lecture 13: Sequential Logic Counters and RegistersCountersIntroduction: CountersAsynchronous (Ripple) CountersAsynchronous Counters with MOD number < 2nAsynchronous Down CountersCascading Asynchronous Counters
CS1104-13Lecture 13: Sequential Logic: Counters and Registers3Lecture 13: Sequential Logic Counters and RegistersSynchronous (Parallel) CountersUp/Down Synchronous CountersDesigning Synchronous CountersDecoding A CounterCounters with Parallel Load
CS1104-13Lecture 13: Sequential Logic: Counters and Registers4Lecture 13: Sequential Logic Counters and RegistersRegistersIntroduction: RegistersSimple RegistersRegisters with Parallel LoadUsing Registers to implement Sequential CircuitsShift RegistersSerial In/Serial Out Shift RegistersSerial In/Parallel Out Shift RegistersParallel In/Serial Out Shift RegistersParallel In/Parallel Out Shift Registers
CS1104-13Lecture 13: Sequential Logic: Counters and Registers5Lecture 13: Sequential Logic Counters and RegistersBidirectional Shift RegistersAn Application – Serial AdditionShift Register CountersRing CountersJohnson CountersRandom-Access Memory (RAM)
CS1104-13Introduction: Counters6Introduction: CountersCounters are circuits that cycle through a specified number of states.Two types of counters:synchronous (parallel) countersasynchronous (ripple) countersRipple counters allow some flip-flop outputs to be used as a source of clock for other flip-flops.Synchronous counters apply the same clock to all flip-flops.
CS1104-13Asynchronous (Ripple) Counters7Asynchronous (Ripple) CountersAsynchronous counters: the flip-flops do not change states at exactly the same time as they do not have a common clock pulse.Also known as ripple counters, as the input clock pulse “ripples” through the counter – cumulative delay is a drawback.nflip-flops a MOD (modulus) 2ncounter. (Note: A MOD-xcounter cycles through xstates.)Output of the last flip-flop (MSB) divides the input clock frequency by the MOD number of the counter, hence a counter is also a frequency divider.
CS1104-13Asynchronous (Ripple) Counters8Asynchronous (Ripple) CountersExample: 2-bit ripple binary counter.Output of one flip-flop is connected to the clock input of the next more-significant flip-flop.KJKJHIGHQ0Q1Q0FF1FF0CLKCCTiming diagram00 01 10 11 00 ... 4321CLKQ0Q0Q11111000000
CS1104-13Asynchronous (Ripple) Counters9Asynchronous (Ripple) CountersExample: 3-bit ripple binary counter.KJKJQ0Q1Q0FF1FF0CCKJQ1CFF2Q2CLKHIGH4321CLKQ0Q11111000000876511001100Q2000011110Recycles back to 0
CS1104-13Asynchronous (Ripple) Counters10Asynchronous (Ripple) CountersPropagation delays in an asynchronous (ripple-clocked) binary counter.