ONLINE ELECTRICAL ENGINEERING STUDY SITE

Parallel in Serial Out (PISO) Shift Register

In Parallel In Serial Out (PISO) shift registers, the data is loaded onto the register in parallel format while it is retrieved from it serially. Figure 1 shows a PISO shift register which has a control-line (SH/) and combinational circuit (AND and OR gates) in addition to the basic register components (flip-flops) fed with clock and clear pins.n bit parallel in serial out right shift shift register Here SH/ control line is used to select the functionality of the shift register amongst shift or load at a given instant of time. This is because when the SH/ line is made low, A2 AND gates of all the combinational circuits become active while A1 gates become inactive.

Thus the bits of the input data word (Data in) appearing as inputs to the gates A2 are passed on as the outputs of OR gates at each individual combinational circuit. This causes the individual bits of the Data in to be loaded/stored into respective flip-flops at the appearance of first leading edge of the clock (except the bit B1 which gets directly stored into FF1 at the first clock tick). This indicates that all the bits of the input data word are stored into the register components at the same clock tick. Next, SH/ line is driven high to activate the gates A1 of the combinational circuits which inturn disables the gates A2. This causes output bit of each flip-flop to appear at the output of the OR gate driving the very-next flip-flop (except the last flip-flop FFn) i.e. output bit of FF1 (Q1) appears as the output of OR gate 1 (O1) connected to D2; Q2 = output of O2 = D3 and so on. At this stage, if the rising edge of the clock pulse appears, then Q1 appears at Q2, Q2 appears at Q3, … and Qn-1 appears at Qn. This is nothing but right-shift of the data stored within the register by one-bit. Similarly it is seen that for each of the further clock pulses applied, one bit exits the PISO shift register through the output pin of nth flip-flop (Data out = Qn of FFn), which is nothing but the serial output. Thus one requires n clock cycles to obtain the entire n-bit input data word as a serial output of PISO shift register. The truth table of the PISO shift register emphasizing the loading and retrieval processes is shown by Table I, while the corresponding wave forms are shown by Figure 2. data movement in right shift piso shift By slightly modifying the design of Figure 1, one can make the data bits within the register to shift from right to left, thus obtaining a left-shift PISO shift-register (Figure 3). However the basic working principle remains unaltered. n bit parallel in serial out left shift shift register




Closely Related Articles Latches and Flip FlopsS R Flip Flop S R LatchActive Low S R Latch and Flip FlopGated S R Latches or Clocked S R Flip FlopsD Flip Flop or D LatchJ K Flip FlopMaster Slave Flip FlopRead Only Memory | ROMProgrammable Logic DevicesProgrammable Array LogicApplication of Flip FlopsShift RegistersBuffer Register and Controlled Buffer RegisterData Transfer in Shift RegistersSerial In Serial Out (SISO) Shift RegisterSerial in Parallel Out (SIPO) Shift RegisterParallel in Parallel Out (PIPO) Shift RegisterUniversal Shift RegistersBidirectional Shift RegisterDynamic Shift RegisterUninterruptible Power Supply | UPSConversion of Flip FlopsMore Related Articles Digital ElectronicsBoolean Algebra Theorems and Laws of Boolean AlgebraDe Morgan Theorem and Demorgans LawsTruth Tables for Digital LogicBinary Arithmetic Binary AdditionBinary SubtractionSimplifying Boolean Expression using K MapBinary DivisionExcess 3 Code Addition and SubtractionK Map or Karnaugh MapSwitching Algebra or Boolean AlgebraBinary MultiplicationParallel SubtractorBinary Adder Half and Full AdderBinary SubstractorSeven Segment DisplayBinary to Gray Code Converter and Grey to Binary Code ConverterBinary to BCD Code ConverterAnalog to Digital ConverterDigital Encoder or Binary EncoderBinary DecoderBasic Digital CounterDigital ComparatorBCD to Seven Segment DecoderParallel AdderParallel Adder or SubtractorMultiplexerDemultiplexerOR Operation | Logical OR OperationAND Operation | Logical AND OperationLogical OR GateLogical AND GateNOT GateUniversal Gate | NAND and NOR Gate as Universal GateNAND GateDiode and Transistor NAND Gate or DTL NAND Gate and NAND Gate ICsX OR Gate and X NOR GateTransistor Transistor Logic or TTLNOR GateFan out of Logic GatesINHIBIT GateNMOS Logic and PMOS LogicSchmitt GatesLogic Families Significance and Types of Logic FamiliesBinary Number System | Binary to Decimal and Decimal to Binary ConversionBinary to Decimal and Decimal to Binary ConversionBCD or Binary Coded Decimal | BCD Conversion Addition SubtractionBinary to Octal and Octal to Binary ConversionOctal to Decimal and Decimal to Octal ConversionBinary to Hexadecimal and Hex to Binary ConversionHexadecimal to Decimal and Decimal to Hexadecimal ConversionGray Code | Binary to Gray Code and that to Binary ConversionOctal Number SystemDigital Logic Gates2′s Complement1′s ComplementASCII CodeHamming Code2s Complement ArithmeticError Detection and Correction Codes9s complement and 10s complement | SubtractionSome Common Applications of Logic GatesKeyboard EncoderAlphanumeric codes | ASCII code | EBCDIC code | UNICODENew Articles Voltage SensorFlow MeasurementVoltage in ParallelVoltage in SeriesVoltage Regulator 7805How to Use a Digital Multimeter?