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Multimedia Card (MMC) is a portable flash memory card used in digital cameras, mobile phones, etc.

MultiMedia Cards were developed in 1997 by SanDisk and Siemens based on Toshiba NAND memory, have a seven-pin connector (designed to minimize the risk of contact damage), the card consists of a plastic shell and a printed circuit board on which the memory chip is located, microcontroller and contacts. Despite the serial nature of MMC, data and commands can be transmitted simultaneously. MultiMedia Card works with voltage 2.0V-3.6V, but there are also options with lower power requirements. The SD Card is a nine-pin interface developed jointly by Matsushita, SanDisk and Toshiba in 2000.

There is also a Micro Memory Card (MMC), which is structurally identical to the Multimedia Card, but differs in logical layout and is intended exclusively for use in SIMATIC S7 programmable logic controllers from Siemens AG.

Size 24×32×1.5 mm.

Since 2004, also available in a reduced case 24×18×1.5 mm

end of form start of form With a simple mechanical adapter, RS-MMC cards can be used with equipment designed for "full size" MMCs. Dual Voltage Reduced Size MMC (MMCmobile) are also available, which can operate not only on the standard 3 V supply voltage, but also on 1.8 V.

MMC is mostly compatible with the later developed SD card and can be used instead of SD. In the opposite direction, replacement is most often impossible, since SD cards are thicker than MMC and simply mechanically may not enter the MMC card slot.

MMC uses a relatively simple open data transfer protocol, therefore, unlike Secure Digital (SD), it can be used in homemade devices.

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

Depending on the command index, the answer may be not only R1(see set basic commands) on CMD58 response R3(R1 and the terminating 32-bit OCR value), and some commands need more NCR time and they will respond R1b. This is an R1 response followed by a busy flag (the signal on the "DO" line is held low by the card while the internal process continues). The host controller must wait until the end of the process until "DO" goes high (i.e. wait for 0xFF). As well as R2 when requesting the state of the STATUS register.

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 R2 structure table). And the answer R3, respectively, of 5 bytes.

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

The structure of the answer R1.

The structure of the answer R2.

Initialization in SPI mode.

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

After reaching the 2.2 V supply, wait at least a millisecond, set the DI and CS lines high and give about 80 pulses to the CLK pin. After this procedure, the card will be ready to accept the native team.
Send command CMD0 (soft reset). The card should respond (R1) with the pending bit (0x01) set.
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 the correct 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.

command 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 rowwith established high levels on the lines DI and CS.

After being idle for more than 5 ms, the memory card enters a 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 card status.

For SDC cards in case of command rejectionCMD1 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 block of data.

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

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

Reading a block of data.

The data block reading algorithm 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 (by default 512 bytes) and 2 bytes CRC.

The CRC value is not required, but the acceptance procedure (transmission of 0xFF from the MCU) is required.

Block reading.

Write a block of data.

The algorithm for writing a data block is as follows:

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

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

The CRC value is not required, but the procedure for passing any values is necessary.

You can programmatically not evaluate idle time, but immediately give an initialization command. During software implementation, I encountered an incorrect write, for some reason all bytes were written to the sector with a shift to the left. The problem was solved only by passing the start bit (0xFE) twice.

Block record.

Acknowledgment byte when writing a data block.

Write / read several blocks in a row.

With the help of 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 set, then the read / write process can be stopped by CMD12 commands when reading, as well as by passing the token " Stop Tran" when recording, respectively.

Practical use.

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

The year is taken as the last two digits - 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 (to avoid collision outside the sector boundary) - this is the third, middle byte of the memory card sector address.
The lower, 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 address of the sector and read from the card. With this method, data can be stored for several years. True, there are drawbacks, there is quite a lot of unused space. Although, if desired, you can use for other tasks.

Who needs to throw off a code fragment in assembler for 18 peaks.

Questions can be asked at..

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 actual amount of memory that the card has differs from the theoretical maximum that 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, the actual amount of memory is 10% less than promised.

Speed

Speed is fun. The faster the card, the less time it takes to write data to the card. A fast card will allow the camera to take more pictures in a shorter 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 designation 1x means a speed of 150 KB per second.

Reliability

According to testing, xD and Compact Flash cards are the most secure. Modern cards The memory is designed for several write-rewrite cycles, which ensures the safety of data 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

Prices for memory cards vary accordingly depending on the parameters listed above and the "brand name".

Brand

The choice of manufacturer (brand) of memory cards often plays a big role for customers. Fan sentiment is especially strong among young people and amateur photographers. There is a huge amount of opinions, tests, disputes about which manufacturer of memory cards is the best! According to the results of some tests - the fastest cards Memory Kingston, according to the results of other Transcend maps. Someone considers Microdia the most reliable brand, someone Sandisk. As in the case 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 support the Compact Flash card. The Compact Flash CF card is ideal for photography enthusiasts. In fact, no card can boast such speeds and volumes as the Compact Flash card. To date, Compact Flash cards have a capacity of 2 MB to 128 GB. The most popular "size" Compact Flash 16Gb and 32Gb. In terms of speed, the Compact Flash 600x and Compact Flash 667x are this moment are the fastest cards in the series. But not only the speed of Compact Flash became the key to its popularity. Compact Flash type has one of the most optimal volume/price ratios.

As technology has advanced, this format has evolved. CompactFlash Type II (CF Type II) characterized by an increased read / write speed and a slightly greater thickness. Digital equipment with a CompactFlash Type II slot also supports a Compact Flash card.

The most famous Compact Flash CF manufacturers 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's not exactly a memory card, but rather a miniature hard drive. Compactflash Microdrive has a housing and a connection connector similar to Compact Flash II. However, the disadvantages of CF Microdrive - such as increased power consumption and heat dissipation, low performance, sensitivity to vibrations - are slowly pushing it out of the market. Of the pluses - the Microdrive card has a fairly low price in relation to its volume. The size of the compactflash Microdrive ranges between 170 MB and 8 GB. The Microdrive card is integrated into some devices: Apple iPod mini - 4GB and 6GB Hitachi Microdrive, HTC Athena 8GB Hitachi Microdrive, iriver H10 - 5GB and 6GB Seagate Microdrive, etc. The file system of the CF Microdrive is 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 the Secure Digital card are its small size, high write and read 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 the 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 capacity of 32GB and Secure Digital XC (SDXC) up to 2TB.

For miniature technology developed formats 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, as their compactness allows 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 you to issue 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. Among the advantages of the xD-Picture card are its compactness, reliability, speed, and low power consumption. Cons: Together with the Sony Memory Stick, this is one of the most expensive memory cards out there. 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 fully fit into the SM slot. There is a limit on the size of the used xD card (128, sometimes - 256 MB), and there may also be limitations in the operation of the reader.

smart media is a portable flash memory card developed by Toshiba, Olympus and Fuji. At the moment, the SmartMedia card has almost completely disappeared from circulation. Very rarely there are only Japanese digital cameras (for example, Olympus) of the last 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 low price and compactness. The disadvantages are a small amount of built-in memory (128 MB SmartMedia cards are the limit), the lack of a memory controller to reduce the price, mechanical insecurity and a short service life (no more than 5 years). The SmartMedia memory card exists 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 Sony company exclusively for its products. That is why Sony Memory Sticks are the most expensive cards on the market, sharing the first place with xD. Sony Memory Stick is not even one, but a whole family of memory cards. It also includes Memory Stick Pro, a faster option, and Memory Stick Duo, a smaller and more expensive card. Memory Stick Pro Duo are used in camcorders, digital cameras, personal computers, printers, game consoles PSP and some Sony Ericsson mobile phones.

The capacity of the 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 (8-16GB). All of them 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 Memory stick PRO for use in HDTV cameras. And a little later - in 2008 - the Memory Stick PRO Duo Mark 2 card was released, 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 (besides 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 players. 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. Advantages of MultiMedia Card - small size, as well as a solid mechanical design and low power consumption. Among the drawbacks of the Multi Media Card is the slow interface and rather high cost. The MMC multimedia card is mostly compatible with the later developed SD card and can be used instead of SD.

The development of the secure digital MultiMedia card has led to the creation of Reduced Size—Multi Media Card (RS-MMC). RS-MMC memory card half the size standard map MMC, and its weight is 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 capacity 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 models of Nokia smartphones only support DV-RS-MMC cards Compatibility: RS-MMC \ DV-RS-MMC -> MMC -> SD (with adapter).

Memory cards MMC Plus appeared in 2005, their main difference from SD and MMC cards is high data transfer speed (up to 52 Mb/s). Map MMC Plus HC(High Capacity) is an extension of MMCPlus. The capacity of this model is 4GB. Distinctive feature 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 the cell phone will not sit down so quickly.

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

Introduction One of the observed trends among memory cards, in addition to the self-evident increase in their performance, is their further miniaturization, in the light of which the prospects for the most popular CompactFlash media until recently seem increasingly vague. In this article, we will try to evaluate the performance of two MMC and SD memory cards from one of the largest manufacturers of Pretec Corporation. But not only they will become the object of our attention. In such delicate matter As a clarification of the real speed of memory cards, devices that read information from them always pay very significant attention to the final results. Unfortunately, we have to determine the speed of reading and writing compact media indirectly, and not directly. The "superfluous" link in the chain becomes a card reader, which has its own characteristics. It is he who, in most cases, is the reason that we are unable to achieve the performance of memory cards declared by manufacturers. For this reason, we were particularly interested in the new Pretec card reader, which we decided to compare in efficiency with the SanDisk device we used earlier. In order to get a more objective picture here, we decided to re-measure the performance of the previously tested memory card A-DATA Turbo SD, which then showed not so high results that one could count on, based on the declared characteristics.

Pretec e-Disk II USB Card Reader

This time we decided to start introducing the participants with the new e-Disk II card reader. At first glance, it may seem that you are dealing with a regular USB flash drive, so this miniature drive is similar to this category of devices in terms of appearance and sizes. However, upon closer contact, it becomes clear that this is not the case. In a "streamlined" case made of translucent blue plastic, under a hinged cover, there is a compartment for installing memory cards of two categories.

Under the removable cap, which, however, continues to hang on a thin metal chain, a USB connector is found. At the end of the chain there is an oval metal plastic with the name of the manufacturer and a miniature "carbine", thanks to which you can use the card reader as a regular keychain. Finishing the description of this memory card reader, we can also mention the presence of an LED indicator of the operating mode.

Among those not named specifications It should be noted that the USB 2.0 interface is supported. Naturally, this stylish card reader can be used not only for its intended purpose for reading SD and MMC memory cards, but also as a regular USB flash drive. To do this, you just need to leave one of the above-mentioned media in it. :)

Estimated retail price of the card reader is $11.

Pretec MMC Plus 1 GB

The memory card of the MMC Plus family that came to us did not have the inscription 266x on it, indicating the transfer speed, which would allow it to be completely identified with the media presented on the manufacturer's website. There is no mention of speed characteristics on the packaging either. In such a situation, our testing is of particular relevance and will help to establish the truth.
The estimated retail price of a 2 GB memory card is $150.

Pretec SD 133x 2 GB

The Secure Digital card family includes media from 256 MB to 4 MB. The declared transfer speed of 133x indicates the achievement of the milestone of 20 Mb / s. Memory cards are based on SLC NAND technology (65 nm).
Estimated retail price of a 2 GB memory card is $170.

Test Methodology

List of programs used for testing:

FC-Test version 1.0;
AIDA version 3.95.

During operation, the test platform of the following configuration was used:

Motherboard - Albatron PX865PE Pro;
Central processor - Intel Pentium 4 2.4 GHz;
Hard disk - IBM DTLA-307015 15 GB;
Graphics adapter - Radeon 7000 32 MB;
RAM - 256 MB;
Operating system - Microsoft Windows 2000 with Service Pack 4.

Media testing was performed using a SanDisk ImageMate 5-in-1 Reader/Writer and a Pretec e-Disk II Card Reader.

FC Test

During the test using the FC-Test program, the real performance characteristics of memory cards were found out, and, in this case, through their results and the efficiency of the card readers we are interested in. Using this utility, we reproduced situations associated with the use of three patterns that reflect the influence of sizes (1, 10, and 100 MB) and the number of files (1, 10, and 100) on media performance.

First, let's see how media behaves when using a pattern consisting of one hundred files of one megabyte.

The first diagram shows the results of measuring the speed of writing (creating) files. In the case of using the SanDisk card reader, Pretec's SD media is in first place, slightly ahead of its opponent in the person of the A-DATA card. We won't be making a direct comparison between different types of media, but note that Pretec's MMC Plus was way behind the other two testers in terms of write speed.
The use of Pretec's e-Disk II card reader brings a wonderful transformation to hitherto slow devices. All media show a sharp increase in write speed. This is especially evident on the example of the MMC Plus card, the performance of which is increased by almost six times, allowing it to rise to the very top of the diagram. The increase in speed is also very noticeable for the other two SD media. To a greater extent, this applies to the Pretec product.

The chart with the results of measuring the speed of reading one hundred files per megabyte, in the case of using a SanDisk card reader, suggests that both SD media show almost the same performance in this indicator, but the Pretec product is slightly ahead. The map noticeably lags behind them in terms of reading speed MMC memory.
Using a Pretec card reader to test media allows you to get more than a noticeable increase in performance for all three participants. This looks especially impressive with the MMC memory card. Her reading speed increased sixfold. A good "gain" was also obtained from SD media, which again demonstrated almost the same results with a slight advantage of the Pretec card. The read speed of both SD media has almost doubled.

Now let's move on to considering the situation associated with using a pattern consisting of ten files of ten megabytes.

In the graph of the media write speed results using the SanDisk card reader, we can see that Pretec's SD memory card is slightly ahead of A-DATA's product. The MMC carrier shows a very modest result.
In the case of using a Pretec card reader as a working device, all media again have a "second wind". The MMC memory card "transforms" the most. She has almost a sixfold increase in write speed. Pretec's SD media almost doubles its performance and is well ahead of its opponent, the A-DATA Turbo SD card.

In the next diagram, we see that reading files from media in a SanDisk card reader leads to the fact that both SD memory cards have complete equality of results. The MMC media still shows consistently slow write speeds.
The use of the new Pretec card reader for reading files once again led to a very significant increase in the performance of all three media. The SD card reading speed is equal to each other and about twice as fast as when using a SanDisk card reader. The performance of the MMC media has increased by about six times.

It's time to take a look at the performance of media, shown in the case of working with a pattern consisting of one large 100 MB file.

In the chart with the speed of writing a file to memory cards, the results obtained using a SanDisk card reader indicate that the Pretec SD media has slightly outperformed its opponent. The MMC memory card has a very slow performance.
Replacing the card reader with a Pretec device results in a noticeable increase in write speed for all media. This is especially pronounced with the MMC memory card. Its performance has increased by about six times. Among SD cards, Pretec's card reader replacement hit the hardest, with its write speed roughly doubling to outperform a similar type of media made by A-DATA.

The graph with the results obtained in the course of measuring the reading speed of devices shows that in the case of using a Sandisk card reader, there is full speed parity between SD cards and a very noticeable lag in this indicator of MMC media.
Once again, we also see the beneficial effect of the Pretec card reader on the reading speed of all three media we tested. The speed of SD memory cards has increased by about two times, and the performance of MMC media has increased by about six times.

AIDA32

The second stage of our testing is related to the measurement of media performance indicators using the AIDA32 program. During the synthetic tests, we filmed graphs of linear reading and writing, as well as access time. Corresponding diagrams were constructed based on the averages of these three parameters.

Pretec MMC Plus: SanDisk ImageMate 5-in-1