How to choose a memory card?

It is worth highlighting a number of points that affect the choice of a memory card:

Memory card capacity

It is important to know that the real memory capacity of the card differs from the theoretical maximum, which is written on the package. This is due to the fact that part of the card is occupied by service information: file data, service information, information to protect the memory card from failures, etc. On average, real memory capacity is 10% less than promised.

Speed

Speed ​​is fun. The faster the card, the less time it will take to write data to the card. A fast card will allow the camera to take more pictures in a short amount of time. Super, Ultra, Pro, Xtream memory cards are faster than other cards. Per unit of speed is selected. The speed of the 133x card is twice as fast as the 66x card. The 1x designation means a speed of 150 KB per second.

Reliability

According to the tests, the most secure cards are xD and Compact Flash cards. Modern memory cards are designed for several write-overwrite cycles, which ensures data integrity for a period of at least 5 years.

Protection

Many memory cards, such as SD, Memory Stick, have the ability to protect information from illegal use.

Memory card prices

The prices for memory cards vary accordingly, depending on the parameters listed above and the "name of the brand".

Brand

The choice of the manufacturer (brand) of memory cards often plays a big role for customers. Fan mood is especially strong among young people and amateur photographers. There is a colossal number of opinions, tests, disputes about which memory card manufacturer is the best! Based on some tests as Kingston's fastest memory cards, and on other Transcend cards. Someone considers the most reliable brand Microdia, someone Sandisk. As in the case of mobile phones, there is no unequivocal opinion on this matter.

Types of memory cards

Compact Flash (CF)- one of the oldest and most common types of memory cards. The format was developed by SanDisk Corporation in 1994. Most digital cameras, PDAs, MP3 players and other devices have support for Compact Flash cards. The Compact Flash CF card is ideal for photography enthusiasts. In fact, no card can boast such speeds and capacities as a Compact Flash card. Today, Compact Flash cards range in size from 2 MB to 128 GB. The most popular Compact Flash "size" is 16Gb and 32Gb. In terms of speed, Compact Flash 600x and Compact Flash 667x are currently the fastest cards in the series. But not only the speed of Compact Flash has become the key to its popularity. Compact Flash type has one of the most optimal volume / price ratios.

With the development of technology, this format has evolved. CompactFlash Type II (CF Type II) characterized by increased read / write speed and somewhat greater thickness. Digital technology with a CompactFlash Type II connector also supports a Compact Flash card.

The most famous manufacturers of Compact Flash CF are A-DATA, ATP, Canon, FujiFilm, Kingston Technology, Kodak, Lexar, Memorex, Olympus, Panasonic, PNY, Ritek, SanDisk, Samsung, Sony, Toshiba, Transcend, Verbatim Corporation, UMAX.

Microdrive — it is not really a memory stick, but rather a miniature hard drive. Compactflash Microdrive has the same housing and connector Compact Flash II. However, CF Microdrive's disadvantages - such as increased power consumption and heat dissipation, low speed, sensitivity to vibrations - are slowly pushing it out of the market. On the plus side, the Microdrive card has a fairly low price in relation to its volume. The compactflash Microdrive ranges between 170 MB and 8 GB. Microdrive is integrated in some devices: Apple iPod mini - 4GB and 6GB Hitachi Microdrive, HTC Athena 8GB Hitachi Microdrive, iriver H10 - 5GB and 6GB Seagate Microdrive, etc. File system CF Microdrive - NTFS.

Secure Digital (SD) Is a joint development of Panasonic, Toshiba and SanDisk. At the moment, Secure Digital card is one of the most common data storage formats. The advantages of a Secure Digital card are its small size, high read and write speed, low power consumption, the ability to protect the information stored on it from copying, accidental erasure or destruction, and mechanical strength. The standard file system for Secure Digital SD cards is FAT32. The maximum speed of a Secure Digital card is 300x (i.e. 45000 KB / s). Secure Digital memory does not exceed 4 GB.

The expansion of the Secure Digital card has led to the emergence of additional formats - Secure Digital HC (SDHC) with a maximum volume of 32GB and Secure Digital XC (SDXC) with a volume of up to 2TB.

For miniature equipment, formats have been developed MiniSD(21.5x20x1.4 mm), MicroSD(11x15x1 mm) and MicroSDHC(11x15x1 mm), which have adapters (adapters), with which they can be inserted into any slot for a regular SD card. Cards of this size are usually used in cell phones, since their compactness makes it possible not to increase the size and weight of modern devices.

MiniSDHC(Mini Secure Digital High Capacity) - is an extension of the miniSD format and allows the production of memory cards with a capacity of 4 GB or more. However, they are only compatible with MiniSDHC-enabled devices.

xD-Picture- developed in 2001 by well-known manufacturers of digital photographic equipment Olympus and Fuji. The advantages of the xD-Picture card include its compactness, reliability, speed, and low power consumption. Disadvantages: Together with the Sony Memory Stick, this is one of the most expensive memory cards. The xD memory card is only found in Olympus and Fuji digital cameras. In addition, xD Picture memory is suitable for storing digital movies. Compatibility: xD -> Compact Flash (with adapter).

There is an external adapter that allows xD-Picture cards to be used in the SmartMedia slot, but it does not fit completely into the SM slot. There is a limitation on the size of the xD card used (128, sometimes 256 MB), and there may also be limitations in the operation of the reader.

SmartMedia Is a portable flash memory card made by Toshiba, Olympus and Fuji. At the moment, SmartMedia card has almost completely disappeared from circulation. It is very rare to find only Japanese digital cameras (for example, Olympus) of the past years of release with support for Smart Media. But Olympus limits the functionality of non-native cards, and their purchase will cost significantly more. The advantages of the card include its low price and compactness. The disadvantages are the small amount of built-in memory (SmartMedia cards are 128 MB - the limit), the absence of a memory controller for the sake of reducing the price, mechanical insecurity and a short service life (no more than 5 years). The SmartMedia memory card is available in two versions - 5 V and 3.3 V, they differ only in the position of the cut corner.

Memory Stick- Unique cards based on flash memory technology developed by the world famous company Sony exclusively for its products. This is why Sony Memory Sticks are the most expensive cards on the market, sharing the top spot with xD. Sony Memory Stick is not even one, but a whole family of memory cards. It also includes a Memory Stick Pro, a faster version, and a Memory Stick Duo, a more compact and expensive card. Memory Stick Pro Duo is used in camcorders, digital cameras, personal computers, printers, PSP game consoles and some SonyEricsson mobile phones.

The capacity of a Memory Stick has never exceeded 128 MB, as well as Memory Stick Duo(also no more than 128MB). More advanced in this matter Memory Stick PRO(1GB) and Memory Stick PRO Duo (8-16 GB). They all differ in size, however, there are special adapters for connecting modules of one type to a slot of another type.

Cards Memory Stick Pro-HG Duo were announced at the end of 2006. This is a high-speed version of the Memory stick PRO for use in HDTV cameras. And a little later - in 2008 - the Memory Stick PRO Duo Mark 2 was published, the volume of which was 16 GB.

Micro Memory Stick- has a very small size (15 x 12.5 x 1.2 mm). Designed for use in Sony Ericsson mobile phones. The advantage of microMMC (in addition to its size) is that the information on it is protected from unauthorized copying.

MultiMediaCard (MMC)- became the first memory card designed specifically for use in mobile phones and iPods. MMC appeared in 1997 thanks to the efforts of Sandisk and Siemens. The first MMC memory cards were actively promoted by mobile phone manufacturers Nokia and Siemens. The MultiMedia Card benefits from its small footprint, robust mechanical design and low power consumption. The disadvantages of the Multi Media Card include a slow interface and a rather high cost. The MMC multimedia card is for the most part compatible with the later developed SD card and can be used instead of SD.

The development of secure digital MultiMedia card has led to the creation Reduced Size - Multi Media Card (RS-MMC). The RS-MMC memory card is half the size of a standard MMC card and weighs only 1g. An adapter is required to ensure compatibility with the existing MMC standard when using RS-MMC cards. In terms of speed, they are similar to MMC cards, the maximum volume of which today is 2 GB. RS-MMC is found in some Nokia and Siemens models.

There is also a modification of these cards called DV-RS-MMC, this card consumes less power, as a result the phone will have to be charged less often. It is also worth noting that some Nokia smartphones only support DV-RS-MMC cards. Compatibility: RS-MMC \ DV-RS-MMC -> MMC -> SD (with adapter).

Memory cards MMCPlus appeared in 2005, their main difference from SD and MMC cards is the high data transfer rate (up to 52 Mb / s). Map MMCPlus HC(High Capacity) is an extension of MMCPlus. The capacity of this model is 4GB. A distinctive feature of the MMCPlus HC is that it can only be used with compatible devices. And in devices without support, it works like a standard MMC.

microMMC- designed for mobile devices with ECC support. (Error Checking and Correction - detection and correction of errors when writing / reading). The advantage is low power consumption, so that the cell phone will not sit down as quickly.

MiCard (Multiple Interface card) Is a multi-interface card developed by Taiwan Industrial Technology Research Institute, compatible with existing USB ports as well as MMC card slots. This is a new type of card, the advantage of which is the high data transfer rate (480 Mbps). MiCard is used to directly transfer data between a portable device and a desktop computer without connecting a card reader.

No sooner had we gotten used to cards that comply with the SD 1.1 specification (and most devices still only support the slower SD 1.0), when a transition to SD 2.0 loomed on the horizon. It can be assumed that, as a result, 1.1 becomes a "passable" version, and you shouldn't pay attention to it. In fact, everything is different. There is a feeling that the implementation of SD 2.0 will be even slower and more painful than the transition from 1.0 to 1.1, or even from MMC 3.0 to 4.x. Most likely, this process will resemble the transition from MMC to SD, which, by the way, did not end as a result - instead of the MMC death predicted many times (including me), this format, on the contrary, has recently found a second wind. The reason is the same - the lack of backward compatibility between SD and SDHC (such a logo will be worn by all cards that meet specifications 2.0). If an SD 1.1 card can be safely used in conjunction with devices designed for SD 1.0 (albeit at a lower speed - as much as possible in 1.0), the same applies to MMC 4.x / 3.0, then the SDHC card will work in "normal" There will be no SD device. Thus, an SD 1.1 or MMCplus card could be bought for the future, but an SDHC card could not. At the same time, SDHC devices will be compatible (when available) with regular SD cards, so the latter can be safely purchased. Not the fact that you will lose something later. Why? Let's see what SD 2.0 brings us.

Just fixing bugs

The transition from SD 1.0 to 1.1 doubled the maximum speed of work, the transition from MMC 3.0 to 4.0 gave us, in fact, new cards, but what does SD 2.0 give? Officially, there are only two things - an increase in the maximum volume of cards and the Class Speed ​​Rating. The second is simpler, so let's start with it.

As you know, manufacturers prefer to label memory cards according to the maximum read speed, and the theoretically possible one. Not all and not always, but in most cases we observe exactly this. The recording speed, if indicated, is also maximum, and even then not always, and only in the specifications and in small print. And the speed of reading (the notorious "X") is most often indicated directly on the map in arshin (compared to the size of the map itself) letters. However, it is far from always at least close to the write speed (a vivid example is MLC chips, where the difference is several times by definition), and it is difficult to achieve high values ​​of the latter in the case of flash. Manufacturers do not indicate it - it is unprofitable. As a result, the purchased "high-speed" card can easily turn out to be slower than the "regular" one, which we have met more than once. At the same time, in many areas of application, the reading speed is not very important (just think - photos after the vacation will be transferred to the computer in 10 minutes, and not in 5: no one dies), while the write speed is critical. An example is the same cameras, where a low write speed simply does not allow for continuous shooting. The situation is even worse with video recording, where flash is gradually becoming one of the most commonly used media: a low write speed will make shooting simply impossible due to the fact that most frames will "drop out" with an obvious end result. The first attempt to sort out the mess with markings was made by the MMC-alliance: the MMCplus card is not only obliged to support the 4.x specification, but also to have a minimum steady-state write speed of at least 2 MB / s. The SD-association went even further, introducing three classes of cards: Class 2, Class 4 and Class 6. The numbers here are not abstract values, namely the established minimum write speed - 2, 4 and 6 MB / s. This innovation is useful, but not so vital: our tests show that today the overwhelming majority of even inexpensive cards are quite capable of handling 6 MB / s. On the other hand, it will become easier when buying: for example, if you know that SDHC Class 6 is required to fully realize the capabilities of a photo or video camera, then you should look for such a card without rummaging through the test results and descriptions on the manufacturers' websites. Of course, the possibility of abuse on the part of the manufacturer remains in theory, but in this case he will receive not only lamentations from the deceived user in various forums, but also harassment from the Association, which hardly anyone will do (even from small companies).

As for the volume, the situation is simple and straightforward. Officially, today's SD cards cannot exceed 2GB. The limitation is not physical, but logical: this is due to the used file system - FAT16. The latter also supports volumes larger than 2 GB, but with a non-standard cluster size, which the manufacturers of consumer equipment for the most part will not do. And for SDHC, the official file system is FAT32, so the limitation is almost lifted. However, some upper frames have been included in the standard so far - 32 gigabytes, but up to this capacity compact cards will still grow and grow (and prices will fall and fall :)). In the end, some of the formats also support large volumes, but cards of at least 16 GB, let alone 32 or 64, are not yet visible;) So, from this point of view, SDHC is an obvious step forward compared to SD ... However, somewhat blurred by the fact that some hardware manufacturers have already mastered FAT32 support within SD 1.1 as well. And the manufacturers of memory cards responded with the release of SD cards, with a capacity of 4 gigabytes. Such cards, even in our area, already cost less than $ 100. They will subsequently work in equipment with SDHC support (let me remind you that there is compatibility in this direction), and no one will fix devices that do not support such cards anyway, since SDHC will definitely not work in them;)

This is what makes the transition from SD 1.1 to 2.0 unlike the transition from 1.0 to 1.1. In the second case, we could simply buy new cards and wait for the appearance of new devices that would reveal all their capabilities. In the first it is necessary at first wait until the market is saturated with devices with SDHC support, and Then buy cards as they are useless for older devices. Even then, you can still use regular high-capacity SD's as they will work in the future. It is possible that in the present, but it is necessary to check a specific device. So far on the SanDisk website, I have found only seven SDHC-compatible devices with all that it implies. We can say that the recently actively announced SDHC cards with a capacity of 4 GB are simply useless - you can buy an ordinary one with such a capacity. When you want to get an eight gigabyte card, it's another matter: there will be no SDHC alternatives. But first you need to purchase a device in which you can use such a card.

And how can this affect "popular" volumes up to 2 GB? No - SDHC cards of this capacity are not planned. This market segment will remain the fiefdom of SD 1.1, and many users do not even need two gigabytes at the current price level. That is why testing SD 1.1 cards continues to make sense, and this situation can last at least another year, or even more. After the appearance of the specifications of version 4.1, the MMC alliance does not make any sudden movements - first you need to master what the standard already allows (since the latest version of the specification was developed a little later than in the case of a competitor, and it was much more revolutionary than SD 1.1 - in As a result, quite standard MMC 4.x cards with a capacity of 8 GB have already been announced, and nothing in the standard had to be altered;)). The main interest for us is still represented by cards compatible with SD 1.1 and MMC 4.1. We will study these once again. The topic of today's article is representatives of several lines of flash cards from Kingston, belonging to the two mentioned families. In addition to the manufacturer, they are related, by the way, also the capacity - all by gigabyte. For many applications, it is quite enough, and the price has already dropped to such a level that you can not deny yourself anything;)

Meet the test subjects

According to the chronology of creation and alphabet, it is most logical to start with MMCplus - a direct descendant of those good old MMC cards, with a capacity of ten or two megabytes, from which all branches of the family tree of both MMC and SD families began their "pedigree". But the rest, in fact, are lateral shoots, and MMCplus, I repeat once again, is direct, although in its content (and a little in shape - the contact group is completely different) significantly different from the ancestor. However, we've seen a lot of cards of this standard, so I'll let you know that its real capacity, according to Everest, is 973 MB, and let's move on.

MMC cards were originally developed with an eye to maximum compactness, but time has shown that they are too large for some applications. A new shoot sprouted from the tree - RS-MMC cards, which looked like cut off to the length of MMC. Later, DV RS-MMC appeared on their basis, differing in support of supply voltage not only 3.3 V, but also 1.8 V, since energy consumption is directly related to voltage, the need to reduce it in mobile devices is obvious. And after the appearance of the MMC 4.0 specifications, MMCmobile - DV RS-MMC was released with support for new operating modes. If you look from the other side, you can call these cards and RS-MMCplus, fortunately, for full-size models it is also recommended (albeit optional) to support 1.8 V. At first, all RS-modifications were noticeably inferior in capacity to the base ones (for purely technical reasons ), however, as technology develops, prices for high-density flash microcircuits decrease and users' appetite grows (mobile phones, where such cards are in use, have long been competing with digital players with considerable success and are getting closer and closer to the domain of digital cameras), a gap in the case of mass modifications were increasingly reduced. However, I have not yet seen the announcement of an 8 GB MMCmobile, and MMCplus has no problems, but in a retail network (at least in Moscow), both cards are still limited to 2 GB. As I said, we are testing a card with a capacity of 1 GB declared or (according to Everest) 988 MB real.

The Secure Digital standard originated from MMC a long time ago, and is not its direct descendant - the cards are similar, but, strictly speaking, they do not have to be compatible in any direction (however, thanks to the manufacturers of consumer equipment, we can often use both, but this is achieved using dual-standard controllers). Nominally, two versions of the specifications have changed (and they existed at different times), but, as I wrote at the beginning of the article, version 1.1 will not disappear anywhere in the near future, and it will never go anywhere from cards up to 2 GB. We are testing just a gigabyte card, and not a simple one, but an "extreme" one. However, the speed limit from the point of view of Kingston is at 133x, and some manufacturers have mastered even 150x, but the latter can mean anything in practice, and the promised 20 MB / s, at least for read operations, is now quite real. How real they are in our case - tests will show. I will only say that an attempt to achieve technical perfection and create universal cards for all applications played a bad joke with Secure Digital: virtually no one uses this very secure, but it eats the capacity of the card. According to Everest, Kingston's gigabyte SD card is only 941MB in size.

The use of flash cards in small-sized technology, as I said, led to the flourishing of their smaller modifications. If the MMC-alliance focused on RS-MMC / MMCmobile, then miniSD cards were an alternative from the SD-association. It should be noted that the position of the Alliance is slightly better - in the case of MMC cards are physically and electrically compatible in terms of the slot. The SD Association did not cut it off, but came up with a new form factor compatible with the "ancestor" only with the help of special adapters. And so the features are the same - reduced size and reduced supply voltage. The capacity has been reduced for a long time, but now both SD and miniSD are equally constrained by the limitations of the standard, that is, 2 gigabytes (in practice, nevertheless, there is a difference - "non-standard" cards with twice the capacity in the case of SD exist, but nobody can make such miniSDs did not dare). By the way - the real capacity, which is the funniest thing, in our case is larger for miniSD: 949 MB according to Everest :)

And now we will measure your boy- used to say the hero of one cult cartoon. The cards, of course, are not boys (and not girls :)), and I am not the postman Pechkin, but nowadays there is no way without measurements.

Testing methodology

Testing was carried out on a computer with the following configuration:

• EpoX 8NPA SLI
• AMD Athlon 64 3200+ (512K L2)
• 1 GB PC3200 DDR SDRAM
• system hard drive Western Digital WD740GD
• card reader Apacer MegaSteno AM230
• Windows XP Pro + SP2

To measure the parameters of the subjects, the program Lavalys Everest Ultimate Edition 2006 2.80 was used, or rather, the disk drive test included in it.

Competitors

Since our cards are of different standards, the diagrams will show everything that we have previously tested on this card reader. At the same time, among other things, we will once again compare the capabilities of MMC 4.x and SD 1.1 with each other: yet we have not tested so many of them so far to deny ourselves the pleasure :)

Reading tests

Nobody managed to repeat the record of the ultra-fast MMCplus card from Apacer in this case. Kingston MMCplus, judging by the results, supports only four data lines and the mandatory (from the point of view of the standard) clock frequency of 26 MHz. MMCmobile is noticeably faster (most likely due to the utilization of the entire possible bus width), but it falls short of high-speed SD cards. On the other hand, both SD and miniSD cards with a speed of 133x reach the results, despite the fact that no one announced a record speed for the latter.

The access time for reading for most cards has long been within the range of 0.5-1.5 ms. Our today's test subjects were no exception. As a funny grimace of fate, one can regard the fact that their results are arranged in alphabetical order, despite the alternation of formats in it :)

Write tests

miniSD lags far behind the full-sized card, although it works quite quickly. SD showed exactly the same result as 133x from Pretec - sometimes, it turns out, you can pay attention to Xs. In the MMCplus / MMCmobile pair, the positions have changed: judging by the speed, the second card uses MLC chips with all that it implies. And for the first, the read and write speeds do not differ, which works in favor of the theory of the narrowness of the data bus - the flash microcircuits themselves would have “gotten” more, but they are not given it.

With one exception, write access times are as expected. However, an exception deserves a separate mention: the write access time for SD Ultimate is lower than for the fastest hard drives, although the opposite picture is observed for most flash drives (as you can see in the diagram). This result is not unique - the Pretec i-Disk Diamond flash drive “responds” quickly. At this rate, soon all flash drives will overtake their magnetic counterparts in all performance parameters;) Still, the problem with a limited number of rewriting cycles should be solved, the price should be reduced, and that's it - solid-state drives will play a death march to their competitors :)

Real capacity

Above (in the description of the cards) I indicated it, but for convenience of comparison I will repeat it in the table:

What conclusions can be drawn? Firstly, you shouldn't rely on the declared capacity - the real one is much less. Secondly, even within the framework of the products of one company of the same standard, it can differ markedly. Thirdly, what I paid attention to, the capacity of MMC cards, all other things being equal, is higher than that of SD: nothing is given for nothing in this world. The difference between the minimum and the maximum in today's testing reaches 47 MB ​​- quite recently cards with a lower total capacity were quite a mass product (smaller ones still often invest in a set of cameras);)

Prices

The table below shows the average retail prices of cards tested today in Moscow, relevant at the time you read this article:

MMCplus	MMCmobile	Secure digital	miniSD
N / A (0)	N / A (0)	N / A (0)	N / A (0)

Total

Not too long ago, we became convinced that MMC cards can be much faster than SD cards. Today we have seen not the first confirmation that they are not always faster, even under ideal conditions. In old equipment, everything will be even worse for MMC - high-speed SD cards can lose their speed by two times, while high-speed MMCs can "sink" by more than an order of magnitude.

As for the actual Kingston cards, they all demonstrate very decent speed indicators, even when they were not promised (when they promised, the reality corresponds to the promises). At the same time, they are distinguished by a democratic price, which, coupled with the popularity of this brand and a good warranty period, makes them a very reasonable candidate for purchase. Everything. And which ones - depends on your preferences (or rather, the preferences of your digital equipment) in terms of tires and form factors.

Various memory cards are typical examples of external flash drives. Today, many of the devices in our use, such as: cell phones, cameras, media and MP3 players and others, use memory cards as information carriers.
We believe that it will not be superfluous to know the features that various types of memory cards have, each of which is designed for a specific device.

What's inside these cards ...

Flash memory is a type of data storage, the main purpose of which is to increase the functionality of modern mobile devices. This allows manufacturers to lead the market and produce equipment demanded by users. A huge advantage of memory cards is the absence of additional power requirements, they are content with what is already in the device where they are used. Kara memory is easily filled with information and just as easily released from it. There are no mechanical moving parts in it, therefore it requires a minimum of power and its life is practically unlimited. Memory cards allow you to rewrite information from tens of thousands of cycles to a million.

The storage period of data on these devices is quite long and ranges from 20 to 100 years. Another plus is its low sensitivity to external influences, vibrations and shocks.

But one of the biggest advantages of memory cards is their compactness. With a thickness of three millimeters or less, the card has a maximum length of only four centimeters.

Variety of varieties

In the documentation for your device, there is always a description or abbreviation of the type of memory cards that this device can use. Having decided on the type of card, choose a manufacturer, focusing on the most famous and already proven manufacturers. Some of them have memory cards equipped with various adapters that significantly increase functionality and allow the memory card to be used in other devices.

Today there are seven main types of memory cards.
CompactFlash, otherwise CF, consisting of two types - CF type I and CF type II. These types of memory cards are the most common because of their characteristics, which sharply distinguish them from other types of compact storage media. Possessing a high speed of data exchange and providing a fairly high amount of memory, these cards have, in aggregate, a very low price in relation to megabytes / ruble, which is very attractive for both those who produce mobile devices and those who use them. According to all available data, it is currently the most common type of memory card.

IBM Microdrive- another type of memory cards for which the format does not quite fit this definition Compact Flash type II due to the fact that it is practically a reduced copy of the hard drive. Having a cost much lower than other types of memory cards, but it is a less reliable device due to moving parts. Another negative aspect of this card is its higher power consumption. Therefore, rare manufacturers use this variety in their products, the connectors of which correspond to CF type II.

SmartMedia- is also a representative of inexpensive and compact flash cards (only up to one millimeter thick). The low cost of these cards is primarily determined by the use of available components, but this, in turn, is also a disadvantage, since the use of inexpensive components can lead to abnormal cases and can cause loss of information.

Multimedia Card (MMC)- This is, perhaps, one of the best representatives of this class of memory cards. The main advantages of this type of memory cards are their small size and low power consumption. True, all this affects the speed of information exchange. The dimensions of these cards are 24x32x1.4 mm, and the short one is 24x18x1.4 mm. They are used mainly in cell phones and other devices, which are very compact in size.

SecureDigital (SD)- With their dimensions these memory cards are slightly inferior to MMC, but they are more preferable from the point of view of the speed of information exchange when working with a large size of the stored data. This feature dictates higher prices for them.

MicroSD- practically in terms of its characteristics it is not inferior to SD, while having a smaller size. Almost all memory cards of this type come with SD /

SD and MMC are backward compatible, so MMC memory cards can be installed and operated instead of SD, but the reverse is alas - impossible. Moreover, in the latest versions of devices manufactured by manufacturers (phones, players), only an SD-type connector is installed in order to introduce the versatility of the card (it is even indicated in the documentation as an SD / MMC connector).

MemoryStick- specially made and used practically only in devices manufactured by Sony. The dimensions of this memory card are 24 * 32 / 1.4 (2.1) mm. The card is very protected from tampering, and its performance is very similar to a SecureDigital (SD) memory card. However, its weak point is the small amount of stored information.

According to the latest statistics, currently the most common, generally accepted and used are memory cards of types CompactFlash and SD / MMC.

For the convenience of assessing the appearance and dimensions of various types of cards, we will show them clearly:

1 = MMC Plus (Multimedia Card)
2 = SD Mini (Secure Digital)
3 = SD Micro (Secure Digital)
4 = MMC Mobil (Multimedia Card)
5 = MS Pro (Memory Stick Pro)
6 = MS Pro Duo (Memory Stick Pro Duo)
7 = RS MMC (Multimedia Card)
8 = SM (Smart Media)
9 = CF (Compact Flash)
10 = SD (Secure Digital)

What should you choose after all? ...

As a rule, this task is one of the easiest, you just need to know what type of memory cards can be used in the device you purchased. You can easily find out from the documentation for your device or from the inscriptions on the case. The only thing that you personally can do is choose a manufacturer based on your preferences.

What volume...?

In general, the question is trivial. You can count by the number of photos, music or video time, but as a rule, whatever you choose, it always becomes small.

The most important thing is to determine how much you are willing to spend on it; for most, the choice decreases several times at once. Indeed, with a large amount of stored information, a high rate of exchange, minimal dimensions, the price may be too high for you to be able to afford it. So just choose the largest amount you can afford.

As you can see from the figure, after transmitting the command frame, it is necessary to continue reading bytes (Ncr) from the microSD until the response (R1) is received, while the CS level must be active "0".

Depending on the command index, the answer may not only be R1(see basic command set) on CMD58's answer R3(R1 and the trailing 32-bit OCR value) and some commands need more NCR time and they will respond with R1b... This is the R1 response followed by the busy flag (the signal on the "DO" line is held low by the card while the internal process continues). The host controller must wait for the process to finish until "DO" goes high (ie, wait for 0xFF). And also R2 when requesting the status of the STATUS register.

The R1 response contains 1 byte, its structure can be seen in the table below. The R2 response consists of two bytes, the first byte R1 and the second R2 (see the table of the structure of R2). And the answer is R3, respectively, from 5 bytes.

R1 response with a value of 0x00 means successful completion of the command, otherwise the corresponding flag will be set.

R1 response structure.

R2 response structure.

Initialization in SPI mode.

After resetting and energizing, the card is set by default to the MMC (Serial Peripheral Interface) protocol mode; to switch to SPI mode, do the following:

1. After reaching the supply of 2.2 V, wait at least a millisecond, set the DI and CS lines to a high level and send about 80 pulses to the CLK pin. After such a procedure, the map will be ready to accept its own team.
2. Send command CMD0 (soft reset). The card should respond (R1) with the wait bit set (0x01).
3. Send command CMD1 (to start card initialization). Wait for a 0x00 response to confirm the completion of the process initialization.

Let me remind you that the CMD0 command must contain a valid CRC field. It makes no sense to calculate, since there are no arguments in this command, therefore it is constant and has a value of 0x95. When the card enters SPI mode, the CRC function will be disabled and will not be checked. The CRC option can be re-enabled with the CMD59 command.

As a result, the CMD0 command will look like this: 0x40.0x00.0x00.0x00.0x00.0x95.

• team index - 0x40.
• argument is 0x00.0x00.0x00.0x00.
• CRC-0x95.

As for 80 pulses, they can be generated by transmitting the value 0xFF via SPI10 times in a rowat set high levels on the lines DI and CS.

After idle time for more than 5 ms, the memory card goes into power-saving mode, and is only able to receive commands CMD0, CMD1 and CMD58. Therefore, the initialization process (CMD1) must be repeated almost every time when reading / writing a data block or checking the status of the card.

For SDC cards in case of command rejectionCMD1 it is recommended to use the ACMD41 command.

The initialization process itself can take a relatively long time (depending on the size of the card) and can reach hundreds of milliseconds.

Reading and writing a data block.

By default, in SPI mode, the exchange between the microcontroller and the card is carried out in blocks of 512 bytes, therefore, to write even one byte, you will first have to read the entire block and, after changing the byte, rewrite it back. The block size can be changed in the CSD register of the memory card.

To avoid addressing errors when executing read / write commands, it is necessary that the address is clearly indicated at the beginning of the sector. To do this, you can clear the "0" bit of the 3 bytes of the sector address, i.e. make it even, and the lowest value should always be 0x00.

Reading a block of data.

The algorithm for reading the data block is as follows:

• After confirming the initialization, we send the CMD17 command (response R1), with the address of the required sector.
• We send 0xFF before receiving the start byte 0xFE.
• We accept a data block (512 bytes by default) and 2 bytes of CRC.

The CRC value is optional, but an acceptance procedure (transfer of 0xFF from MCU) is necessary.

Reading a block.

Writing a block of data.

The algorithm for writing a data block is as follows:

• If the card idle time was more than 5 ms, we send the CMD1 command (R1 response).
• After confirming the initialization, we send the CMD24 command (response R1), with the address of the required sector.
• We transmit the start byte 0xFE.
• We transfer a data block (512 bytes by default) and 2 bytes of CRC.
• We receive a byte of confirmation of the record.
• We are waiting for the end of the recording (changing the byte 0x00).

The data block can be less than 512 bytes when changing the block length with the CMD16 command.

The CRC value is optional, but the procedure for passing any values ​​is necessary.

Downtime estimation can be omitted programmatically, but immediately issue an initialization command. In software implementation, I encountered an incorrect write, for some reason all the bytes were written to the sector with a left shift. The problem was solved only by transmitting the start bit (0xFE) two times.

Block recording.

Acknowledgment byte when writing a data block.

Writing / reading several blocks in a row.

Using commands CMD18, CMD25 you can read / write several blocks in a row or the so-called multi-block read / write. If the number of blocks has not been specified, then the read / write process can be stopped by CMD12 commands when reading, as well as by passing a token " Stop Tran"when recording, respectively.

Practical use.

The practical application of memory cards is quite wide. In its latest design, I used microSD to record readings from various sensors (temperature, alarms) every hour during the day. The data is saved as follows:

• The last two digits are taken - this corresponds to the first (main) byte of the memory card sector address.
• Month, two digits - this corresponds to the second, most significant byte of the memory card sector address.
• Day, two digits are multiplied by 2 (in order to avoid hitting outside the sector boundary) - this is the third, middle byte of the memory card sector address.
• The least significant, fourth byte, respectively, is always "0".

As a result, the search for data by date is simplified, it is enough just to translate the request to the sector address and read from the card. With this method, the data can be stored for several years. True, there are drawbacks, there is a lot of unused space. Although, if desired, it can be used for other tasks.

Who needs to skip a piece of assembler code for 18 picks.

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