Sequential and Clocked Circuits; Finite State MachinesSequential Circuits (Recap.)Recap: D Flip FlopTiming DiagramWhat controls the “Write” signal?Synchronous Sequential Circuit (aka Clocked Sequential Circuit)ShorthandsClock SpeedsWhat limits clock speed?Finite State MachinesState diagram for automatic door Implementing as synchronous circuitImplementationMoore FSM (see handout)Other examples of FSMsPortion of Genghis AFSM Network [Parker’94]Meet the little green man…Discussion:How would you implement a Turing-Post program with a digital circuit?Sequential and Clocked Circuits; Finite State Machines3/28/2006COS 116Instructor: Sanjeev AroraSequential Circuits (Recap.) Circuits with AND, OR and NOT gates. Cycles are allowed. Can exhibit “memory”. May exhibit instabilities (saw last time).Recap: D Flip FlopBasic Memory Block – stores 1 bit.a.k.a. “Airlock”, “Master-Slave”DWMIf we “toggle” the write input (setting it 1 then setting it 0) then M acquires the value of D.Timing Diagram5V0VTimeD5V0VTimeW5V0VTimeMWhat controls the “Write” signal?Synchronous Sequential Circuit(aka Clocked Sequential Circuit)Combinational CircuitCLOCKOne or more D FlipflopsINPUTSShorthandsCombinational CircuitOne or more D FlipflopsCLKClock SpeedsHeinrich Hertz1857-941974 Intel 8080 2 MHz(Mega = Million)1981 Original IBM PC 4.77 MHz1993 Intel Pentium 66 MHz2005 Pentium 4 3.4 GHz(Giga = Billion)Distance traveled by light during 1 clock cycle of Pentium 44 inchesWhat limits clock speed?Finite State MachinesState diagram for automatic door ClosedOpenDetected PersonNo Person DetectedDetected PersonNo Person DetectedImplementing as synchronous circuitINPUTSTATE0 = No Person Detected1 = Person Detected0 = Door Closed1 = OpenClosedOpenDetected PersonNo Person DetectedDetected PersonNo Person DetectedClosedOpenDetected PersonNo Person DetectedDetected PersonNo Person DetectedInput Present State Next State00 010 101 011 1ImplementationDWMINPUTCLOCK0 = No Person Detected1 = Person Detected0 = Door Closed1 = OpenSTATEMoore FSM (see handout)InputsCircuit to computenext stateFlip flops(memoryelements)Circuit tocomputeoutputsCLKK Flip flops allow FSM to have 2KstatesOther examples of FSMs Sisyphus Brook’s Genghis (51 FSMs) (see p. 46 in our text) Human Soul a la Aquinas (see Handout)Portion of Genghis AFSM Network[Parker’94]IRsensorsprowlbeta forcewalkfor/bakpitchbetabalanceup legtriggerleg downsteerbeta posfeeleralphacollidealphaadvancealphabalancealpha posSSSIDIÆreceive input from sensorsÆcontrol actuatorsÆduplicated twiceÆunique; “central control”Finally... How computers execute programs.Scribbler Control Panel ProgramMachine Executable CodeF5“Download to Robot”(Compilation)Meet the little green man…The Fetch – Decode – Execute FSMExecuteDecodeFetchCircuit to computenext stateFlip flops(memoryelements)Circuit tocomputeoutputsCLKProgram stored in machine memory; each instruction represented by say 64 bits…..........0110100000110111101010111…………………….Discussion:How would you implement a Turing-Post program with a digital circuit? 1.PRINT 0 2. GO RIGHT 3. GO TO STEP 1 if 1 SCANNED 4. GO TO STEP 1 if 0 SCANNED 5. STOPAssume “PRINT” and “SCAN” as basic
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