Shift Registers: Types, Applications, and Design
TRAVEL LOG
A digital circuit is a sequential circuit (i.e., the values of their outputs depend on their inputs and previous values) consisting of a series of bistable elements, usually of type D, connected in cascade (Fig. 1), which pivot synchronously with the same clock signal.
TYPES OF SHIFT REGISTERS
Depending on the type of inputs and outputs, shift registers are classified as:
- Series-Series: Only the entry of the first flip-flop and the output of the latter are accessible externally. They are used as digital delay lines and synchronization tasks.
- Parallel-Series: Entries are accessible to all flip-flops, but only the output of the latter. Usually, there is also a serial input, which only alters the content of the first flip-flop, and can function as the previous group.
- Series-Parallel: Accessible the outputs of all flip-flops, but only the first entry. This and the previous rate are used to convert serial data into parallel and vice versa, for example, as the RS232 serial connections.
- Parallel-Parallel: Both entries and exits are accessible. They are used for arithmetic calculations.
APPLICATIONS
In addition to the series-parallel conversion and parallel-serial shift registers, they have other typical applications:
- Pseudorandom Generator: It is constructed with a shift register, feeding back to the input a combination of multiple outputs, usually an exclusive OR between them.
- Multiplier Series: Multiplication is performed by addition and displacement. One example is the 74LS384.
- Register of Successive Approximations: Used for A/D converters, calculating the bit is going on, starting with the most significant. Using a DAC converter compares the analog input to the partial results, generating the next bit.
- Delay: It can be used to slow a bit an integer number of clock cycles (consisting simply of a set of flip-flops in cascade, as many as we want to slow clock cycles the bit).
WAYS TO MAKE SHIFT REGISTERS
You can build shift registers as follows (if you do not dispose of them and do other combinational circuits and sequential):
SYNCHRONOUS
In this type of flip-flops, the external clock signal is connected to all flip-flops. This ensures that all the bistable elements evolve simultaneously, and therefore there is no time lag or transient.
ASYNCHRONOUS
At this rate, the clock signal connects only to the first flip-flop, while the other inputs are connected to the output of the previous bistable element.
EXTENSION COUNTER
A cascade consists of as many flip-flops as the number of bits that we want the counter to have, taking the external clock signal to the first of them and the output of each flip-flop to the clock input of the next.
Time Sequence
In a digital counter, the delay binary output is formed when each flip-flop is activated to a particular clock pulse; it is actually a frequency division.
The digital clock uses counters and frequency dividers and accumulators.
The Memory Unit
A digital computer’s memory unit can be classified by operational type or storage. An operational circuit is capable of storing binary information in its flip-flops and combinational gates and is also capable of performing work as data processing.
Random Access Memory
This is memory where the processor receives instructions and stores results. It is the work area for most of a computer’s software.