"For all purposes of the embedded system based on a microcontroller, which are the main elements in the memory. For example, developers need enough RAM to store all volatile variable, and create a buffer management for a variety of applications stack .RAM embedded system is important, the same, developers need a space for storing the application code, a non-volatile data and configuration information.
However, the problem lies in the non-volatile memory technology continues to expand, many choices, so choose the right memory applications challenging.
In this paper, a variety of memory technologies have been introduced and the ON Semiconductor, Adesto Technologies, Renesas, ISSI, Cypress Semiconductor, Advantech, GigaDevice Semiconductor and Silicon Motion and other vendors introduced products, for example, to help developers understand the various types of memory characteristic. Additionally, this article discusses the application of the best types of memory, so that the effective use of the developer.
Embedded Systems EEPROM and FRAM
EEPROM is often the first to developers, most often considered for memory devices embedded systems. In embedded applications, such non-volatile memory generally used to store system configuration parameters. For example, the connection to the CAN bus network devices might CAN ID is stored in the EEPROM.
The following characteristics EEPROM makes it ideal for embedded systems developers:
Small package size
Relatively affordable price
A typical range of bit rates of 100 kbps to 1000 kbps
Standardized electrical interface
Usually supports I2C and SPI interface
Currently, the Digi-Key website EEPROM can be found in a quick search, a total of nine suppliers 5,800 EEPROM variety of EEPROM. For example, ON Semiconductor of CAT24C32WI-GT3 is a 32 Kb (4 KB) EEPROM devices, an 8-lead SOIC package, speeds up the I2C bus is connected at 1 MHz (FIG. 1).
FIG 1: ON Semiconductor of CAT24C32WI-GT3 is a 1 Kb of EEPROM, through I2C or SPI port connected to the microcontroller and configured to store application data. (Source: ON Semiconductor)
Notably, some microcontrollers also includes EEPROM. For example, Renesas the R7FS128783A01CFM # AA1 32-bit microcontroller with on-board EEPROM 4 KB available to developers.
Thus, the configuration requirements can not exceed 4 KB, otherwise, developers need to use an external memory device, or use a flash EEPROM microcontroller to analog to expand capacity.
Although EEPROM favored, but there are some potential pitfalls:
Erase / write operation life is usually 1,000,000
Write cycle is about 500 ns
Writing a single data unit requires multiple instructions
Data retention period of 10 years (a recent product up to 100 years)
Susceptible to radiation and high operating temperatures affect
EEPROM suitable for many applications, but for applications requiring high reliability, developers automotive, medical or aerospace systems are more reliable and want to use the FRAM memory solutions.
FRAM is an abbreviation of "ferroelectric random access memory," compared to the EEPROM memory, an advantage:
Faster (write cycle is less than 50 ns)
Write longer life (up to 1 trillion, EEPROM only 100 million times)
Lower power (operating voltage of only 1.5 V)
Greater radiation tolerance
FRAM memory capacity and relatively EEPROM. For example, Cypress Semiconductor series of FRAM capacity ranges from 4 Kb to 4 Mb. Wherein, FM25L16B-GTR capacity of 16 Kb (FIG. 2). The device 8 lead SOIC, operating frequency up to 20 MHz.
FIG 2: Cypress series of FRAM memory capacity range, and may be configured to store application data from a 4 Kb to 4 Mb connected by SPI microcontroller. FM25L16B-GTR operating frequency (as shown) up to 20 MHz. (Source: Cypress Semiconductor)
For high-end products, Cypress Semiconductor introduced CY15B104Q-LHXIT, a capacity of 4 Mb, supports interface speeds up to 40 MHz (Figure 3). The FRAM memory has the following features:
151 years data retention
100 trillion times the read / write
Direct replacement for serial flash and EEPROM
As you can guess, FRAM EEPROM expensive than the price, so choose the time for memory applications, be sure to weigh all the factors working environment of the device carefully.
FIG 3: CY15B104Q-LHXIT 4 Mb is a device at frequencies up to 40 MHz. Cypress FRAM devices belongs to the family of products, the capacity ranges from 4 Kb to 4 Mb. (Source: Cypress Semiconductor)
Embedded flash memory, eMMC and SD card
Flash embedded systems have many different uses. First, the external flash can be used to extend the internal flash memory, thereby increasing the available memory space of the application code. The solution is used: the use of GD25Q80CTIGR like GigaDevice Semiconductor SPI Flash Module (FIG. 4). If the microcontroller supports the SPI interface, the internal memory can be extended using the 8 Mb GD25Q80CTIGR through the interface.
Figure 4: GigaDevice Semiconductor Limited GD25Q80CTIR the flash memory, the internal space of the flash to extend through the SPI port 8 Mb. (Source: GigaDevice Semiconductor Limited)
Secondly, external flash can be used to store configuration information or application data, instead of an EEPROM or FRAM. In order to reduce costs or extended BOM internal memory to store application data, you may use an external flash memory chips. The microcontroller peripherals and memory may be configured to map the art to more easily access to the external flash memory is added in order to develop, without special drivers needed to customize the call, to connect EEPROM or FRAM.
Adesto Technologies AT25SF161 external flash memory device of the example (FIG. 5) a suitable for this purpose. The device uses a queue of formula SPI (QSPI) interface. QSPI is an extension of a conventional SPI protocol, the system increases the data throughput. For a single transaction need to store or retrieve large number of applications, developers may pay attention to the data of these devices.
QSPI eliminating CPU intervention QSPI peripherals and interfaces from the standard 4-pin (MOSI, MISO, CLK and CS) was changed to 6-pin (CLK, CS, IO0, IO1, IO2, IO3). Thus, four pins available for input and output, but with only two conventional SPI pins.
FIG 5: Adesto Technologies AT25SF161 the external flash device may be used to extend the internal flash memory, having a QSPI interface, faster data storage and retrieval. (Source: Adesto Technologies)
Finally, a flash memory may be used for storing applications and data payload information. For example, GPS systems often do not attempt to store all GPS maps to the local processor, but the use of an external storage device or SD card eMMC devices. These storage media may be SPI or SDIO interface dedicated microcontroller, so as to effectively connect the external storage device.
For example, introduction of ISSI IS21ES04G-JCLI eMMC can be directly connected to microcontroller SDIO interface, its flash memory (FIG. 6) of the extension 32 Gb.
FIG 6: ISSI of eMMC capacity of the flash memory module 32 Gb, can be connected to the host via SPI or SDIO. (Source: ISSI)
In terms of the electrical interface, SD card and eMMC device indistinguishable. In other words, although the two different packages, but all have common pin can be used to connect the microcontroller. However, these two very different types of memory. Compared to the SD card, eMMC usually with the following differences:
More durable, less prone to physical damage
Faster interaction
More expensive
Shall be soldered to the circuit board, not removable
If the user without having to remove memory, use eMMC may provide a more reliable solution, but it still depends on the final application. In either case, developers need to carefully select the memory, because the memory characteristics of each section varies.
For example, the memory may be required after a vehicle subsystem reliability verification standards are often higher than the standard flash memory device. In this case, the developer needs to select the memory automotive identified by, for example, a Silicon Motion SM668GE4-AC 4 GB eMMC module.
When you purchase an SD card, developers must be carefully considered, because, like eMMC, the characteristics of each section of the SD card varies. Developers need to carefully check the card's speed rating and operating temperature. For example, most of the SD card rated temperature range is from 0 to 70 ℃, applicable to consumer electronics.
In addition, each card has an associated memory speed grades, used to describe the expected maximum interface speed. For example, in applications requiring the storage of the image, a Class 2 memory card is slow, much less specifically designed for high-definition video Class 10 memory card, for example, introduction of Advantech SQF-MSDM1-4G-21C SQFlash 4 GB microSD card.
FIG 7: Advantech of SQF-MSDM1-4G-21C SQFlash microSD card memory capacity of 4 GB, high speed rating of Class 10. (Source: Advantech Corp)
Memory Select Tips and Tricks
Choose the right type of memory products for embedded interfaces and challenging. When choosing memory for your application, developers can refer to the following "tips and tricks":
Clear memory working conditions, such as:
Expected erase / write cycles
Temperature, vibration, radiation and environmental conditions and factors
Loading Requirements
Minimum bit rate recording applications a working memory, the required bit rate and maximum bit rate
Select the desired type memory interface closest to the recording bit rate
For automotive or aerospace harsh environmental conditions systems, must be selected or identified by automotive radioresistance strong memory
Use breakout board connected to the selected memory device to the microcontroller to test its performance Development Kit
The above tips will help ensure that developers find memory for embedded applications.
Summarize
Now, the type of nonvolatile memory device of choice for many developers, may be used to store various data, application code from the configuration information, and so forth. As noted above, application developers need to carefully assess the needs carefully choose the type of memory and interfaces, in order to strike a balance between those needs and costs. "
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