Applications of Flip-Flops

Applications of Flip-Flops:

Some of the common uses of the Flip-Flops are as follows:

  • 1)   Bounce elimination switch
  • 2)   Latch
  • 3)   Registers
  • 4)   Counters
  • 5)   Memory, etc.

Some examples of uses of Flip-Flops are given below:

A)  Bounce elimination switch :

Mechanical switches are employed in digital system as a input devices by witch digital information (0 and 1) is entered into the system. There is a very serious problem associated with these switches which is switch bouncing (chattering).

If we entered input as ‘1’ in a sequential circuit the output is ‘1’ but it oscillates between ‘1’and ‘0’ before come to rest i.e. 1. This changes the output of the sequential circuit and creates difficulties. This problem is eliminated by the use of Bounce elimination switches.

B)  Registers :

A register is composed of a group of flip-flops to store a group of bits (word). For storing N bit of words we require N number of flip-flops (one flip of for each bit).

A flip flop can store only one bit of data, a 0 or a 1; it is referred to as a single bit register. When more bits of data are to be stored, a number of flip flops are used. A register is a set of flip flops used to store a binary data. The storage capacity of a register is a number of bits of digital data that it can retain. Loading a register means setting or resetting the individual flip flops, i.e. inputting data into the register so that their states correspond to the bits of data to be stored. Loading may be serial or parallel in serial loading, data is transferred into the register in serial form, i.e. one bit at a time, whereas in parallel loading, the data is transferred into the register in parallel form meaning that all the flip flops are triggered into their new states at the same time. Parallel input requires that the SET and/or RESET controls of every flip flop be accessible.

C)  Counters :

Digital counters are used for count the events. Electrical pulses corresponding to the event are produced using transducers & these pulses counted using a counter.

A digital counter is a set of flip-flops whose stated change in response to pulses applied at the input to the counter. The flip flops are interconnected such that their combined state at any time is the binary equivalent of the total number of pulses that have occurred up to that point. Thus, as its name implies, a counter is used to count the pulses. A counter can also be used as a frequency divider to obtain waveforms with frequencies that are specific fractions of the clock frequency. They are also used to perform the timing function as in digital watches, to create time delays, to crate non-sequential binary counts, to generate pulse trains, and to act as frequency counters, etc.

D)  Random access memory:

In computers, digital control systems, information processing systems it is necessary to store digital data and retrieve the data as desired.

Flip-Flops can be used for making memories in which data can be stored for any desired length of time and then readout whenever required.

The data stored in RWMs (Read Write memories) constructed from semiconductor devices will be lost if power is removed. Such memory is said to be volatile. But ROM is non-volatile. Random access memory (RAM) is the memory whose memory locations can be accessed directly and immediately. By contrast, to access a memory location on a magnetic tape, it is necessary to wind or unwind the tape and go through a series of addresses before reaching the address desired. Therefore, the tape is called the sequential access memory.

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Classification of Memory in computer

Classification of memory

This section provides a classification of memories. There are two main types of memories i.e. RAM and ROM. Following tree diagram shows the classification of Memory:

Classification of memory
Classification of memory

ROM (Read Only Memory):

The first classification of memory is ROM. The data in this memory can only be read, no writing is allowed. It is used to store permanent programs. It is a nonvolatile type of memory. The classification of ROM memory is as follows:

a) Masked ROM: the program or data are permanently installed at the time of manufacturing as per requirement. The data can not be altered. The process of permanent recording is expensive but economic for large quantities.

b) PROM (Programmable Read Only Memory): The basic function is same as that of masked ROM. but in PROM, we have fuse links. Depending upon the bit pattern, the fuse can be burnt or kept intact. This job is performed by PROM programmer.

To do this, it uses high current pulse between two lines. Because of high current, the fuse will get burnt; effectively making two lines open. Once a PROM is programmed we cannot change connections, only a facility provided over masked ROM is, the user can load his program in it. The disadvantage is a chance of regrowing of the fuse and changes the programmed data because of aging.

c) EPROM (Erasable Programmable Read Only Memory): the EPROM is programmable by the user. It uses MOS circuitry to store data. They store 1’s and 0’s in form of charge. The information stored can be erased by exposing the memory to ultraviolet light which erases the data stored in all memory locations. For ultraviolet light, a quartz window is provided which is covered during normal operation. Upon erasing it can be reprogrammed by using EPROM programmer. This type of memory is used in a project developed and for experiment use. The advantage is it can be programmed erased and reprogrammed. The disadvantage is all the data get erased even if you want to change single data bit.

d) EEPROM: EEPROM stands for Electrically erasable programmable read only memory. This is similar to EPROM except that the erasing is done by electrical signals instead of ultraviolet light. The main advantage is the memory location can be selectively erased and reprogrammed. But the manufacturing process is complex and expensive so do not commonly used.

RAM (Random Access Memory):

The second classification of memory is RAM. The RAM is also called as read/write memory. The RAM is a volatile type of memory. It allows the programmer to read or write data. If the user wants to check the execution of any program, user feeds the program in RAM memory and executes it. The result of execution is then checked by either reading memory location contents or by register contents.

Following is the classification of RAM memory. It is available in two types:

a) SRAM (Static RAM): SRAM consists of the flip-flop; using either transistor or MOS. for each bit we require one flip-flop. Bit status will remain as it is; unless and until you perform next write operation or power supply is switched off.

Advantages of SRAM:

  • Fast memory (less access time)
  • Refreshing circuit is not required.

Disadvantages of SRAM:

  • Low package density
  • Costly

b) DRAM (Dynamic RAM): In this type of memory a data is stored in form of charge in capacitors. When data is 1, the capacitor will be charged and if data is 0, the capacitor will not be charged. Because of capacitor leakage currents, the data will not be held by these cells. So the DRAMs require refreshing of memory cells. It is a process in which same data is read and written after a fixed interval.

Advantages of DRAM:

  • High package density
  • Low cost

Disadvantages of DRAM:

  • Required refreshing circuit to maintain or refresh charge on the capacitor, every after few milliseconds.

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