LSN 12 Shift Registers Department of Engineering Technology
LSN 12 Shift Registers Digital circuits with data storage and data movement functions Storage capacity is the total number of bits of digital data a register can retain Each stage (flip-flop) can store one bit
LSN 12 Shift Registers Shifting capability of a register allows for the movement of data between stages of a register at a clock edge
LSN 12 Serial-In / Serial-Out Registers Data input serially right most bit first Uses a sequence of flip-flops to provide serial data storage and shifting Connect in series where output of one flip-flop stage connects to the input of the next flip-flop stage
LSN 12 Serial-In / Serial-Out Registers Example: Determine outputs for a given input waveform if initially reset
LSN 12 Serial-In / Serial-Out Registers Common logic block symbol for serial I/O shift register SRG = Shift ReGister
LSN 12 Serial-In / Parallel-Out Registers The output of each stage is available simultaneously on parallel output lines
LSN 12 Serial-In / Parallel-Out Registers Example: Determine outputs for a given input waveform
LSN 12 Parallel-In / Serial-Out Registers Data entered simultaneously to all stages on parallel input lines SHIFT/LOAD input line When LOW, parallel inputs are loaded to the input of each stage and stored on next active clock edge When HIGH, data is allowed to shift between stages and to the output G1, G2, G3 disabled G4, G5, G6 enabled G1, G2, G3 enabled G4, G5, G6 disabled
LSN 12 Parallel-In / Serial-Out Registers Example: Determine output for a given input sequence and based upon the state of the SHIFT/LOAD line
LSN 12 Bidirectional Shift Register Data is able to be shifted to the right or left depending upon gating logic RIGHT/LEFT input line
LSN 12 Bidirectional Shift Register Example: Assuming that Q 0 = 1, Q 1 = 1, Q 2 = 0, and Q 3 = 1 Input line is LOW
LSN 12 Shift Register Applications Time delay Serial in / serial out Delay = n ( 1/f clk ) Number of stages Clock period Example: Determine the time delay for a 4-bit serial to parallel shift register between the input signal and each output signal
LSN 12 Shift Register Applications Parallel-to-serial / serial-to-parallel data conversion Universal Asynchronous Receiver Transmitter (UART) Data transmitted from microprocessor based systems in parallel form Often must communicate with external devices expecting data in serial form UARTs contain a parallel-to-serial converter and a serial-to-parallel converter
LSN 12 Shift Register Counters Shift register with feedback from serial output to serial input Specified sequence of states Johnson Counter Uses the compliment of the output as the feedback term Produces a modulus of 2n, where n is the number of sages Clock Pulse Q0 Q1 Q2 Q3 0 0 0 0 0 1 1 0 0 0 2 1 1 0 0 3 1 1 1 0 4 1 1 1 1 5 0 1 1 1 6 0 0 1 1 7 0 0 0 1
LSN 12 Shift Registers Ring Counter The shift register output is used as the feedback term Load a sequence of bits into the counter and the sequence is shifted one place around the ring at each clock edge Clock Pulse Q0 Q1 Q2 Q3 Q4 0 1 0 0 0 0 1 0 1 0 0 0 2 0 0 1 0 0 3 0 0 0 1 0 4 0 0 0 0 1
LSN 12 Homework Reading Chapter 9.1 9.7 Assignment HW13 Chapter 9, problems 5, 10, 13, 21