Types of ROM

ROM stands for read-only memory, which provides non-volatile storage of information on any physical medium. Based on the method of storing information, ROM can be divided into three types:

1. ROMs based on the magnetic principle of storing information.

The operating principle of these devices is based on changing the direction of the magnetization vector of sections of a ferromagnet under the influence of an alternating magnetic field in accordance with the values ​​of the bits of the recorded information.

A ferromagnet is a substance capable of possessing magnetization at a temperature below a certain threshold (Curie point) in the absence of an external magnetic field.

Reading of recorded data in such devices is based on the effect of electromagnetic induction or magnetoresistive effect. This principle is implemented in devices with moving media in the form of a disk or tape.

Electromagnetic induction is the effect of the generation of electric current in a closed circuit when the magnetic flux passing through it changes.

The magnetoresistive effect is based on a change in the electrical resistance of a solid conductor under the influence of an external magnetic field.

The main advantage of this type is the large volume of stored information and the low cost per unit of stored information. The main disadvantage is the presence of moving parts, large dimensions, low reliability and sensitivity to external influences (vibration, shock, movement, etc.)

2. ROMs based on the optical principle of storing information.

The operating principle of these devices is based on changing the optical properties of a portion of the media, for example, by changing the degree of transparency or reflectance. An example of ROM based on the optical principle of storing information is CD, DVD, BluRay discs.

The main advantage of this type of ROM is the low cost of the media, ease of transportation and the possibility of replication. Disadvantages - low read/write speed, limited number of rewrites, need for a reading device.

3. ROMs based on the electrical principle of storing information.

The operating principle of these devices is based on threshold effects in semiconductor structures - the ability to store and record the presence of charge in an isolated area.

This principle is used in solid-state memory - memory that does not require the use of moving parts to read/write data. An example of ROM based on the electrical principle of storing information is flash memory.

The main advantage of this type of ROM is high read/write speed, compactness, reliability, and efficiency. Disadvantages - limited number of rewrites.

At the moment, other, “exotic” types of permanent memory exist or are at the development stage, such as:

Magnetic-optical memory– memory that combines the properties of optical and magnetic storage. Writing to such a disk is carried out by heating the cell with a laser to a temperature of about 200 o C. The heated cell loses its magnetic charge. Next, the cell can be cooled, which will mean that a logical zero is written to the cell, or recharged with a magnetic head, which will mean that a logical one is written to the cell.

Once cooled, the magnetic charge of the cell cannot be changed. Reading is performed with a laser beam of lower intensity. If the cells contain a magnetic charge, the laser beam is polarized, and the reader determines whether the laser beam is polarized. Due to the “fixation” of the magnetic charge during cooling, magnetic-optical ones have high reliability of information storage and theoretically can have a recording density greater than ROM based only on the magnetic principle of information storage. However, they cannot replace “hard” drives due to the very low recording speed caused by the need for high heating of the cells.

Magnetic-optical memory is not widely used and is used very rarely.

Molecular memory– memory based on atomic tunneling microscopy technology, which allows individual atoms to be removed or added to molecules, the presence of which can then be read by special sensitive heads. This technology was presented in mid-1999 by Nanochip, and theoretically made it possible to achieve a packaging density of about 40 Gbit/cm 2, which is tens of times higher than existing serial samples of “Hard” drives, but the too low recording speed and reliability of the technology do not allow us to talk about practical use of molecular memory in the foreseeable future.

Holographic memory– differs from the existing most common types of permanent memory, which use one or two surface layers for recording, by the ability to record data over the “entire” memory volume using different laser angles. The most likely use of this type of memory is in ROM based on optical information storage, where optical disks with several information layers are no longer a novelty.

There are other, very exotic types of permanent memory, but even in laboratory conditions they balance on the brink of science fiction, so I won’t mention them, we’ll wait and see.

Any electronics are complex devices, the principle of operation of which is not clear to every average person. What is ROM and why is this device needed? Most users today cannot answer this question. Let's try to fix this situation.

What is ROM?

What are ROMs and where can they be used? Read-only storage devices are the so-called non-volatile memory. Purely technically, these devices are implemented in the form of microcircuits. At the same time, we learned what the abbreviation ROM stands for. Such chips are designed to store information entered by the user, as well as installed programs. In ROM you can find everything from documents to pictures. Information on this chip is stored for several months or even years.

Depending on the device used, memory sizes can vary from a few kilobytes on the simplest devices, which have only a single silicon chip, to terabytes. The larger the permanent storage capacity, the more objects it can store. The volume of the chip is directly proportional to the amount of data. If we try to more succinctly answer the question of what ROM is, we can say the following: it is a storage of information that does not depend on constant voltage.

Using hard drives as ROM

So, we have already answered the question of what ROM is. Now let's talk about what ROMs can be. The main storage device in any computer is the hard drive. Today they are in every computer. This element is used due to its wide data storage capabilities. At the same time, there are also a number of ROMs that use multiplexers in their device. These are special microcontrollers, bootloaders and other electronic mechanisms. Upon closer examination, you need to not only understand the meaning of the ROM abbreviation. To understand the topic, you need to decipher other terms.

Addition and expansion of ROM capabilities through the use of flash technologies

If the user does not have enough standard memory capacity, then you can try to take advantage of the expanded information storage capabilities provided by the ROM. This is done through the use of modern technologies, which are implemented in USB drives and memory cards. These technologies are based on the principle of reusable use. To put it simply, information on such media can be erased and recorded again. A similar operation can be performed tens and hundreds of thousands of times.

What does ROM consist of?

The ROM consists of two parts, which are designated as ROM-A and ROM-E. ROM-A is used to store programs, and ROM-E is used to issue programs. Type A ROM is a diode-transformer matrix, which is flashed using address wires. This section of the ROM performs the main function. The filling will depend on the material used in the manufacture of the ROM. For this purpose, magnetic tapes, magnetic disks, punched cards, drums, ferrite tips, dielectrics with their property of accumulating electrostatic charges can be used.

ROM: schematic structure

This electronics object is usually depicted as a device that resembles the connection of a number of single-bit cells. Despite its potential complexity, the ROM chip is very small in size. When storing a certain bit of information, it is sealed to the case (recording a zero) or to the power source (recording a one). To increase the capacity of memory cells, circuits in permanent storage devices can be connected in parallel. This is exactly what manufacturers do in order to obtain a modern product. After all, when using ROM with high technical characteristics, the device will be competitive in the market.

Amount of memory used in various units of equipment

The amount of memory may depend on the type and purpose of the ROM. In simple household appliances like refrigerators or washing machines, installed microcontrollers will be quite sufficient. Something more complex is installed in rare cases. There is no point in using more ROM here. The amount of electronics is quite small. In addition, technology is not required to perform complex calculations. Modern TVs may require something more complex. The pinnacle of ROM circuit complexity is found in computer hardware such as servers and personal computers. In this technique, ROMs contain from several gigabytes to hundreds of terabytes of information.

Mask ROM

If the recording is done when the recording is done using the metallization process and a mask is used, then such a ROM will be called a mask ROM. In them, the addresses of memory cells are supplied to ten pins. A specific chip is selected using a special CS signal. ROMs of this type are programmed at factories. Therefore, producing them in medium and small volumes is inconvenient and unprofitable. However, in large-scale production, such devices will be the cheapest of the ROMs.

This ensured the popularity of this type of device. From the point of view of the circuit design, such ROMs differ from the general mass in that the connections in the memory matrix are replaced with fusible jumpers, which are made of polycrystalline silicon. At the production stage, all jumpers are created. The computer believes that logical ones are written everywhere. However, during pre-programming, increased voltage is applied.

Using it, logical units are left. The jumpers evaporate when low voltages are applied. The computer believes that a logical zero is written there. The same principle is used in programmable read only memory devices. Programmable ROMs or PROMs have proven to be quite convenient from a technological manufacturing point of view. They can be used in both medium and small-scale production. However, these devices also have their limitations. You can only record a program once, after which the jumpers disappear forever.

Due to the inability to reuse the ROM. If you make a mistake, you have to throw it away. As a result, the cost of all manufactured equipment increases. Due to imperfections in the production cycle. This problem has occupied the minds of developers for quite some time. As a way out of this situation, it was decided to develop a ROM that can be programmed repeatedly.

Electrical or UV erasable ROM

Such devices are created on the basis of a memory matrix, in which memory cells have a special structure. Each cell here is a MOS transistor, the gate of which is made of polycrystalline silicon. Somewhat reminiscent of the previous option. The peculiarity of these ROMs is that the silicon in this case is additionally surrounded by a dielectric, which has insulating properties. Silicon dioxide is used as a dielectric.

Here the operating principle is based on the content of the inductive charge. It can be stored for decades. There are some issues with erasing here. For example, an ultraviolet ROM device requires exposure to UV rays from the outside, for example, from an ultraviolet lamp. Of course, from the point of view of ease of use, an electrically erasable ROM design would be the best option. In this case, to activate you just need to apply voltage. This principle of electrical erasure has been successfully implemented in devices such as flash drives. However, such a ROM circuit is structurally no different from a conventional mask ROM with the exception of the cell structure.

Such devices are sometimes also called reprogrammable. However, with all the advantages of devices of this type, there are certain limits to the speed of erasing information. Typically, this operation takes from 10 to 30 minutes to complete. Despite the ability to rewrite, reprogrammable devices have limitations on their use. UV erasable electronics can survive 10 to 100 write cycles. After this, the destructive influence of ultraviolet radiation will become so noticeable that the device will cease to function.

Such elements can be used to store BIOS programs in video and sound cards for additional ports. Regarding the possibility of rewriting, the principle of electrical erasure will be optimal. The number of rewrites in such devices ranges from 100 to 500 thousand. Of course, you can find devices that can do more, but ordinary users have absolutely no need for such supernatural capabilities.

Read Only Memory (Read Only Memory - ROM)

(Read Only Memory - ROM)

Read Only Memory (ROM, Read Only Memory) is non-volatile memory, used to store data that will never need to be changed. The contents of the memory are “hardwired” into the device in a special way during its manufacture for permanent storage. ROM can only be read.

First of all, a program for controlling the operation of the processor itself is written into permanent memory. The ROM contains programs for controlling the display, keyboard, external memory, programs for starting and stopping the computer, and device testing programs.

The most important ROM chip is the BIOS module (Basic Input/Output System) - a set of programs designed to automatically test devices after turning on the computer and loading the operating system into RAM.

The role of the BIOS is twofold - on the one hand, it is an integral element of the hardware, and on the other hand, it is an important module of any operating system.

So, ROM permanently stores information that is written there when the computer is manufactured.

! Non-volatile memory. When the power is turned off, the contents of the ROM are not erased.

The ROM contains:

1. test programs that check the correct operation of the device every time you turn on the computer;
2. programs for controlling the main peripheral devices (disk drive, monitor, keyboard);
3. A boot program that searches for the operating system boot loader on external media. Modern BIOS allow you to boot the operating system not only from magnetic and optical disks, but also from USB flash drives.

Good day.

If you're looking to fill the knowledge gap regarding what a ROM is, you've come to the right place. In our blog you can read comprehensive information about this in a language accessible to the common user.

Decoding and explanation

The ROM letters are capitalized in the wording "read only memory". It can also be equally called “ROM”. The English abbreviation stands for Read Only Memory, and is translated as read-only memory.

These two names reveal the essence of the subject of our conversation. This is a non-volatile type of memory that can only be read. What does it mean?

• Firstly, it stores immutable data laid down by the developer during the manufacture of the equipment, that is, those without which its operation is impossible.
• Secondly, the term “non-volatile” indicates that when the system is rebooted, the data does not disappear from it, unlike what happens with RAM.

Information can only be erased from such a device using special methods, for example, ultraviolet rays.

Examples

Read-only memory in a computer is a specific location on the motherboard that stores:

• Test utilities that check the correct operation of the hardware every time you start the PC.
• Drivers for controlling main peripheral devices (keyboard, monitor, disk drive). In turn, those slots on the motherboard whose functions do not include turning on the computer do not store their utilities in ROM. After all, space is limited.
• A boot program (BIOS), which launches the operating system boot loader when the computer is turned on. Although the current BIOS can turn on a PC not only from optical and magnetic disks, but also from USB drives.

In mobile gadgets, the permanent memory stores standard applications, themes, pictures and melodies. If desired, the space for additional multimedia information can be expanded using rewritable SD cards. However, if the device is used only for calls, there is no need to expand the memory.

In general, now ROM is found in any household appliances, car players and other electronic devices.

Physical execution

So that you can better get acquainted with persistent memory, I will tell you more about its configuration and properties:

• Physically it is a microcircuit with a reading crystal, if included in a computer, for example. But there are also independent data arrays (CD, gramophone record, barcode, etc.).
• ROM consists of two parts “A” and “E”. The first is a diode-transformer matrix, stitched using address wires. Used to store programs. The second is intended for issuing them.
• Schematically it consists of several single-digit cells. When a specific bit of data is written, a seal is made to the case (zero) or to the power supply (one). In modern devices, circuits are connected in parallel to increase the capacity of cells.
• Memory capacity varies from a few kilobytes to terabytes, depending on which device it is applied to.

Kinds

There are several types of ROM, but in order not to waste your time, I will name only two main modifications:

• The first letter adds the word “programmable”. This means that the user can flash the device himself once.

• Two more letters in front hide the wording “electrically erasable”. Such ROMs can be rewritten as much as you like. Flash memory belongs to this type.

In principle, this is all I wanted to convey to you today.

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ROM is a memory in which information, once written, cannot be changed. For example, a program for loading information from external memory into the RAM of a microprocessor system. All types of ROM use the same circuit design principle. Information in ROM is represented as the presence or absence of a connection between the address and data buses.

The conventional graphic designation of ROM is presented in Fig. 26.10.

Fig.26.10. Conventional graphic designation of ROM

Rice. 26.11. ROM circuit

In Fig. 26.11 shows a diagram of the simplest ROM. To implement a ROM, it is enough to use a decoder, diodes, a set of resistors and bus drivers. The ROM in question contains bit words, i.e. its total size is 32 bits. The number of columns determines the word width, and the number of rows determines the number of 8-bit words. Diodes are installed in those places where bits that have a logical value of “0” should be stored (the decoder supplies 0 to the selected line). Currently, MOS transistors are used instead of diodes.

In table Figure 26.1 shows the state of the ROM, the diagram of which is shown in Fig. 26.11.

Table 26.1

Simple ROM state

Word	Binary representation
A0	A1	D1	D2	D3	D4	D5	D6	D7	D8

As a rule, ROMs have a multi-bit organization with a structure of 2 DM. Manufacturing technologies are very diverse - CMOS, n-MOS, TTL(Sh) and diode matrices.

All ROMs can be divided into the following groups: factory-programmable (mask), one-time programmable, and reprogrammable.

In factory-programmable memories(ROM or ROM), information is recorded directly during their manufacturing process using a photomask, called a mask, at the final stage of the technological process. Such ROMs, called mask ROMs, are built on diodes, bipolar or MOS transistors.

The area of ​​use of mask ROMs is the storage of standard information, for example, character generators (codes of letters of the Latin and Russian alphabet), tables of standard functions (sine, quadratic functions), standard software.

Programmable Read Only Memory Devices(PROM, or PROM) – ROM with the possibility of one-time electrical programming. This type of memory allows the user to program the memory chip once using programmers.

PROM chips are built on memory cells with fusible jumpers. The programming process consists of selectively burning fusible links using current pulses of sufficient amplitude and duration. Fusible links are included in the electrodes of diodes or transistors.

In Fig. Figure 26.12 shows a diagram of a PROM with fusible jumpers. It is manufactured with all diodes and jumpers, i.e. in the matrix everything is “0”, and during programming those jumpers whose cells should contain logical “1” are burned out.

Rice. 26.12. Fragment of the PROM circuit

Programmable read-only memories(RPZU and RPZU UV) – ROM with the possibility of multiple electrical programming. IN IS RPZU UV ( EPROM) old information is erased using ultraviolet rays, for which there is a transparent window in the microcircuit housing; in RPZU ( EEPROM) – using electrical signals.

ROM memory cells are built on n-MOS or CMOS transistors. To construct a green cell, various physical phenomena of charge storage at the boundary between two dielectric media or a conducting and dielectric medium are used.

In the first version, the dielectric under the gate of the MOS transistor is made of two layers: silicon nitride and silicon dioxide. This transistor is called MNOS: metal - silicon nitride - oxide - semiconductor. Charge capture centers appear at the boundaries of the dielectric layers. Thanks to the tunneling effect, charge carriers can pass through a thin oxide film and accumulate at the interface between the layers. This charge, which is the carrier of information stored by the MNOS transistor, leads to a change in the threshold voltage of the transistor. In this case, the threshold voltage increases so much that the operating voltage at the transistor gate is not able to open it. A transistor in which there is no charge opens easily. One of the states is defined as a logical one, the second - zero.

In the second option, the gate of the MOS transistor is made floating, i.e. not connected with other elements of the circuit. Such a gate is charged by an avalanche injection current when a high voltage is applied to the drain of the transistor. As a result, the charge on the floating gate affects the drain current, which is used when reading information, as in the previous version with an MNOS transistor. Such transistors are called LISMOP (avalanche charge injection MOS transistor). Since the transistor gate is surrounded by an insulator, the leakage current is very small and information can be stored for quite a long time (tens of years).

In an electrically erasable ROM, a second gate is placed above the floating gate of the transistor - the control gate. Applying voltage to it causes the charge to dissipate on the floating gate due to the tunneling effect. RPOMs have significant advantages over UV RPOMs, since they do not require special ultraviolet light sources for reprogramming. Electric erase memory has practically replaced ultraviolet erase memory.

A fragment of an ROM circuit using two-gate transistors of the LISMOP type is shown in Fig. 26.13. Writing a logical zero is carried out in programming mode using a floating gate charge. Erasing information, i.e. floating gate discharge means writing a logical one. In this case, when a signal is applied along the sampling line, the polled transistors open and transmit voltage U PIT on the read line.

Modern ROMs have an information capacity of up to 4 Mbit at a clock frequency of up to 80 MHz.

26.5. Flash-memory

Basic principles of operation and type of storage elements Flash-memories are similar to PROMs with electrical recording and erasing of information, built on floating gate transistors. As a rule, due to its characteristics, Flash-memory is allocated to a separate class. It erases either all recorded information at once, or large blocks of information, rather than erasing individual words. This makes it possible to eliminate the control circuits for writing and erasing individual bytes, which makes it possible to significantly simplify the memory circuit and achieve a high level of integration and performance while reducing cost.

Fig.26.13. Fragment of the RPOM circuit

Modern trends in the development of electronic devices require a constant increase in the amount of memory used. Today, engineers have access to microcircuits such as volatile memory DRAM, which is characterized by an extremely low price per bit and high levels of integration, and non-volatile Flash-memory, the cost of which is constantly decreasing and tends to the level DRAM.

The need for non-volatile Flash- memory grows in proportion to the degree of advancement of computer systems in the field of mobile applications. Reliability, low power consumption, small size and light weight are obvious advantages of media based on Flash-memory compared to disk drives. Taking into account the constant reduction in the cost of storing a unit of information in Flash-memory, media based on it provide more and more advantages and functionality to mobile platforms and portable equipment that use such memory. Among the variety of memory types, Flash- cell-based memory NAND is the most suitable basis for building non-volatile storage devices for large volumes of information.

Currently, there are two main structures for constructing flash memory: cell-based memory NOR(OR-NOT) and NAND(AND-NOT). Structure NOR(Fig. 26.14, a) consists of parallel-connected elementary information storage cells. This organization of cells provides the possibility of random access to data and byte-by-byte recording of information. Based on the structure NAND(Fig. 26.14, b) is the principle of sequential connection of elementary cells forming groups (one group has 16 cells), which are combined into pages, and pages into blocks. With this construction of a memory array, accessing individual cells is impossible. Programming is performed simultaneously only within one page, and when erasing, access is made to blocks or groups of blocks.

Fig.26.14. Structures based NOR(a) and NAND(b)

As a result of differences in structure organization between memories NOR And NAND are reflected in their characteristics. When working with relatively large amounts of data, memory writing/erasing processes NAND run much faster than memory NOR. Since 16 adjacent memory cells NAND are connected in series with each other without any contact gaps, a high area of ​​cell placement on the chip is achieved, which makes it possible to obtain a large capacity at the same technological standards. The basis of flash memory programming NAND lies the process of electron tunneling. And since it is used for both programming and erasing, low power consumption of the memory chip is achieved. The consistent structure of the cell organization allows for a high degree of scalability, which makes NAND-Flash leader in the race to increase memory capacity. Due to the fact that electron tunneling occurs through the entire area of ​​the cell channel, the intensity of charge capture per unit area is NAND-Flash lower than other technologies Flash-memory, resulting in a higher number of program/erase cycles. Programming and reading are performed sector-by-sector or page-by-page, in 512-byte blocks, to emulate the common sector size of disk drives.

More detailed features of microcircuits Flash-memory can be considered using the example of crystals of the series HY 27xx(08/16)1 G 1M companies Hynix. In Fig. Figure 26.15 shows the internal structure and purpose of the terminals of these devices.

The microcircuit has the following conclusions:

I/O 8-15– data input/output for x16 devices

I/O 0-7– data input/output, address input or command input for x8 and x16 devices;

ALE– enable address latch;

CLE– enable command latch;

– crystal selection;

– read resolution;

– reading/busy (output with open drain);

– recording resolution;

– write protection

V CC- supply voltage;

VSS- general conclusion.

Fig.26.15. External pin diagram (a), pin assignment (b) and block diagram (c) Flash-memory

The address lines are multiplexed with data I/O lines on an 8 or 16-bit I/O bus. This interface reduces the number of pins used and makes it possible to migrate to higher-capacity chips without changing the printed circuit board. Each block can be programmed and erased 100,000 times. The chips have an open-drain read/busy output that can be used to identify controller activity PER (Program/Erase/Read). Since the output is open-drain, it is possible to connect several such outputs from different memory chips together through one pull-up resistor to the positive terminal of the power supply.

Fig.26.16. Memory Array Organization NAND-structures

Memory array NAND-structures are organized in blocks, each containing 32 pages. The array is divided into two areas: main and spare (Fig. 26.16).

The main area of ​​the array is used to store data, while the spare area is usually used to store error correction codes ( ECC), program flags and bad block identifiers ( Bad Block) main area. In 8-bit devices, the pages in the main area are divided into two half-pages of 256 bytes each, plus 16 bytes of the spare area. In 16-bit devices, pages are divided into a main area of ​​256 words and a spare area of ​​8 words.

Cell-based memory NOR has relatively long erase and write times, but has read access to every bit. This circumstance allows the use of such microcircuits for recording and storing program code that does not require frequent rewriting. Such applications could be, for example, BIOS for embedded computers or software for set-top boxes.

Properties NAND-Flash determined the scope of its application: memory cards and other data storage devices. Now this type of memory is used almost everywhere in mobile devices, photo and video cameras, etc. NAND-Flash underlies almost all types of memory cards: SmartMedia, MMC, Secure Digital, Memory Stick

Currently achieved information capacity Flash-memory reaches 8GB, typical combined program and erase speed is up to 33.6 mS / 64 kB at a clock frequency of up to 70 MHz.

Two main areas of effective use Flash-memories are the storage of rarely changed data and the replacement of memory on magnetic disks. For the first direction it is used Flash- memory with address access, and for the second - file memory.

26.6. RAM type FRAM

FRAM– an operational non-volatile memory that combines the high performance and low power consumption inherent in RAM with the ability to store data in the absence of applied voltage.

Compared to EEPROM And Flash-memory, the time for writing data to a memory of this type and the power consumption are much less (less than 70 ns versus several milliseconds), and the resource for write cycles is much higher (at least 10 11 versus 10 5 ... 10 6 cycles for EEPROM).

FRAM should become the most popular memory in digital devices in the near future. FRAM will differ not only in performance at the level DRAM, but also the ability to save data during a power outage. In a word, FRAM can displace not only the slow Flash, but also regular RAM like DRAM. Today, ferroelectric memory finds limited application, for example, in RFID-tags. Leading companies, including Ramtron, Samsung, NEC, Toshiba, are actively developing FRAM. Should be on the market around 2015 n- gigabyte modules FRAM.

Specified properties FRAM provides a ferroelectric (perovskite) used as the dielectric of the storage capacitor of the memory cell. In this case, a ferroelectric memory stores data not only in the form of a capacitor charge (as in traditional RAM), but also in the form of electrical polarization of the ferroelectric crystal structure. A ferroelectric crystal has two states, which can correspond to logic 0 and 1.

Term FRAM has not yet settled down. First FRAM are called ferrodynamic RAM. However, at present, ferroelectrics are used as storage cells and now FRAM often called ferroelectric RAM.

First FRAM had 2 T/2WITH-architecture (Fig. 26.17, a), on the basis of which most modern ferroelectric memory microcircuits are made. This type of cell, in which each bit has an individual reference bit, allows the charge difference to be determined with high accuracy. And thanks to reading the differential signal, the influence of the scatter in the parameters of the cell capacitors is eliminated. Later appeared FRAM with architecture 1 T/1WITH(Fig. 26.17, b). The advantage of microcircuits with such an architecture is a smaller cell area than in conventional circuits and, therefore, a lower cost of the microcircuit per unit of information capacity.

Figure 26.18 shows a block diagram of a ferroelectric RAM ( FRAM) with a capacity of 1 Mbit and a parallel access interface FM 20L 08 companies Ramtron. In Table 26.1. the pins of the microcircuit are shown.

FM 20L 08 is a 128K×8 non-volatile memory that is read and written like standard static RAM. Data safety is ensured for 10 years, while there is no need to think about the reliability of data storage (unlimited wear resistance), system design is simplified and a number of disadvantages of an alternative non-volatile memory solution based on static RAM with battery backup are eliminated. Recording speed and unlimited number of rewrite cycles make FRAM leader in relation to other types of non-volatile memory.

Fig.26.17. Memory cell type 2 T/2WITH(a) and 1 T/1WITH(b)

Fig.26.18. Structural scheme FRAM FM 20L 08