EKT 124 / 3 DIGITAL ELEKTRONIC 1 CHAPTER 3 Sequential Logic/ Circuits: Shift Register

Shift Register Basic shift register function Serial in/Serial out shift registers (SISO) Serial in/Parallel out shift registers (SIPO) Parallel in/Serial out shift registers (PISO) Parallel in/Parallel out shift registers (PIPO) Bidirectional shift registers Shift register applications

Sequential Logic Circuits Combinational outputs Memory outputs Combinational logic Memory elements Inputs Sequential circuit = Combinational logic + Memory Elements Current State of A sequential Circuit: Value stored in memory elements (value of state variables). State transition: A change in the stored values in memory elements thus changing the sequential circuit from one state to another state.

Registers A register is a memory device that can be used to store more than one-bit information A register is usually realized as several flip-flops with common control signals that control the movement of data to and from the registers ……….

Registers An n-bit register is a collection of n D flip-flops with a common clock used to store n related bits. 74LS175 Example: 74LS175 4-bit register 1D 1Q D Q CLR Q /1Q CLK CLR 4Q 3Q 2Q 1Q 74LS175 1D 2D 3D 4D 2Q 2D D Q CLR Q /2Q 3Q 3D D Q CLR Q /3Q 4Q 4D D Q CLR Q /4Q CLK /CLR

Shift Registers Multi-bit register that moves stored data bits left/right ( 1 bit position per clock cycle) Shift Left is towards MSB 1 1 1 LSI Q3 Q2 Q1 Q0 0 1 1 1 LSI Q3 Q2 Q1 Q0 Shift Right (or Shift Up) is towards MSB RSI 0 1 1 1 Q3 Q2 Q1 Q0 RSI 0 1 1 Q3 Q2 Q1 Q0

Basic Shift Register Functions consist of an arrangement of flip-flops important in applications involving storage and transfer of data (data movement) in digital system used for storing and shifting data (1s and 0s) entered into it from an external source and possesses no characteristic internal sequence of states. D flip-flops are use to store and move data

The flip-flop as a storage element When a 1 is on D, Q becomes a 1 at triggering edge of CLK or remains a 1 if already in the SET state When a 0 is on D, Q becomes a 0 at triggering edge of CLK or remains a 0 if already in the RESET state

Basic data movement in shift registers (Four bits are used for illustration. The bits move in the direction of the arrows.)

Types of Shift Registers Serial In / Serial Out Shift Registers (SISO) Serial In /Parallel Out Shift Registers (SIPO) Parallel In / Serial Out Shift Registers (PISO) Parallel In / Parallel Out Shift Registers (PIPO)

Serial In, Serial Out Shift Registers (SISO) D Q CLK · Serial In Clock Serial Out SRG n > SI SO For a n-bit SRG: Serial Out = Serial In delayed by n clock period 4-bit shift register example: Serial in: 1 0 1 1 0 0 1 1 1 0 Serial out: - - - - 1 0 1 1 0 0 Clock:

Serial In, Serial Out Shift Registers (SISO)

Serial In, Serial Out Shift Registers (SISO)

Serial In, Parallel Out Shift registers (SIPO) SRG n > SI 1Q · 2Q nQ D Q CLK · Serial In Clock nQ 2Q 1Q SO Serial to Parallel Converter Example: 4-bit shift register serin: 1 0 1 1 0 0 1 1 1 0 1Q: - 1 0 1 1 0 0 1 1 1 2Q: - - 1 0 1 1 0 0 1 1 3Q: - - - 1 0 1 1 0 0 1 4Q: - - - - 1 0 1 1 0 0 clock:

Serial In, Parallel Out Shift registers (SIPO) Data bits entered serially (right-most bit first) Difference from SISO is the way data bits are taken out of the register – in parallel. Output of each stage is available

Example: The states of 4-bit register (SRG 4) for the data input and clocks waveforms. Assume the register initially contains all 1s

Parallel In, Serial Out Shift Registers (PISO) CLOCK LOAD/SHIFT Serial in 1Q S D Q CLK 1D L 2Q S D Q CLK 2D L Parallel to Serial Converter Load/Shift=1 Di Qi Load/Shift=0 Qi Qi+1 · · · NQ S D Q CLK Serial out ND L

4-bit parallel in/serial out shift register (PISO)

Parallel In, Parallel Out Shift Register (PIPO) CLOCK LOAD/SHIFT Serial In S D Q CLK 1Q 1D L S D Q CLK 2Q 2D L General Purpose: Makes any kind of (left) shift register · · · S D Q CLK NQ ND L

Parallel In, Parallel Out Shift Register (PIPO) Immediately following simultaneous entry of all data bits, it appears on parallel output.

Bi-directional Shift Registers Data can be shifted left Data can be shifted right A parallel load maybe possible 74HC194 is an bidirectional universal shift register

Bi-directional Universal Shift Registers 4-bit Bi-directional Universal (4-bit) PIPO CLK CLR S1 S0 LIN D QD C QC B QB A QA RIN 11 1 10 9 7 6 4 5 3 2 12 13 14 15 74x194 Modes: Hold Load Shift Right Shift Left R L Mode Next state Function S1 S0 QA* QB* QC* QD* Hold 0 0 QA QB QC QD Shift right/up 0 1 RIN QA QB QC Shift left/down 1 0 QB QC QD LIN Load 1 1 A B C D

Four-bit Johnson counters Serial output connected back to serial input The complement of the output (Q’) is fedback into 1st FF.

Five-bit Johnson counters

A 10-bit ring counter Assume initial state: 1010000000

Shift Register Applications State Registers Shift registers are often used as the state register in a sequential device. Usually, the next state is determined by shifting right and inserting a primary input or output into the next position (i.e. a finite memory machine) Very effective for sequence detectors Serial Interconnection of Systems keep interconnection cost low with serial interconnect Bit Serial Operations Bit serial operations can be performed quickly through device iteration Iteration (a purely combinational approach) is expensive (in terms of # of transistors, chip area, power, etc). A sequential approach allows the reuse of combinational functional units throughout the multi-cycle operation

Shift Register Applications Example: Serial Interconnection of Systems CLOCK Control Circuits Control Circuits Receiver Transmitter /SYNC Parallel Data from A-to-D converter Parallel Data to D-to-A converter Serial-to-parallel converter Parallel-to-serial converter Serial DATA n One bit n

Shift Register Applications Example: 8-Bit Serial Adder ... 7 6 5 > x7 x6 x5 x0 y7 y6 y5 y0 FA Cout S Cin A B D Q CLK CLR CLEAR_C z7 z6 z5 z0 CTL Sequential Implementation of: Z[7..0] = X[7..0] + Y[7..0] V

Shift Register Applications Example: The shift register as a time-delay device

Shift Register Applications Example: Simplified logic diagram of a serial-to-parallel converter