By PURPLELEC | 30 October 2023 | 0 Comments
What are the commonly used embedded memories?
Commonly used embedded storage devices include SDRAM, FLASH, E2PROM, large-capacity storage systems (SD cards, U disks, hard disks), etc.
1.SDRAM memory
SDRAM is synchronous dynamic random access memory, usually used as embedded memory, which is equivalent to the memory of ordinary PCs. SDRAM has gone through four generations since its development, namely SDR SDRAM, DDR SDRAM, DDR2 SDRAM and DDR3 SDRAM.
The 1st generation of SDR SDRAM uses a single-ended Single-Ended clock signal, while the 2nd to 4th generations use a differential clock signal that can reduce interference as the clock signal because of its faster operating frequency. This clock signal is the data storage Frequency of.
The first generation of SDRAM is named after the clock frequency. For example, PC100 and PC133 indicate that the clock frequency is 100MHz/133MHz and the data read/write rate is also 100MHz/133MHz. DDR SDRAM starting from the second generation is named after the data read/write rate, and is preceded by a number indicating its DDR algebraic code. For example, PC2700 is DDR333, its operating frequency is 333MHz/2 = 160MHz, and 2700 means the bandwidth is 2.7GB.
2.FLASH memory
SDRAM is the memory of embedded systems, while FLASH can be regarded as embedded hard disk memory, which is mainly used to store data necessary for the operation of embedded systems, such as operating systems and applications.
FLASH currently on the market can be divided into two categories: NOR and NAND. They are named because their internal structures are similar to "NOR gate" and "NAND gate" respectively. Their internal structure, external characteristics and applications are all different. Big difference.
Generally speaking, the capacity of NOR FLASH is not large, usually only a few MB. It can be repeatedly erased and written many times, up to 100,000 to 1 million times. Following the CFI standard, the manufacturer, model, and capacity can be queried through the CFI command. , internal sector layout and other parameters, thereby realizing automatic configuration through software, and it can guarantee that there are no bad blocks, every data bit is valid, and its addressing uses linear complete data and address line encoding.
Therefore, NOR FLASH is usually used as boot memory for embedded systems, burning U-BOOT, etc. NOR FLASH supports on-chip execution, and programs can be executed directly in NOR FLASH. Its usage is almost the same as that of ordinary SDRAM.
3.E2PROM
E2PROM is mainly used to save some small amounts of data or special-purpose data in embedded systems. It usually uses serial communication interfaces and embedded processors for data interaction, such as I2C bus interface, SPI bus interface and 1-wire bus interface, etc. Its capacity usually ranges from a few hundred bytes to several million bytes.
4. Large capacity memory
Large-capacity storage systems in embedded systems include SD cards, USB flash drives and ordinary hard drives, which are usually used to save large-capacity data and interact with embedded processors through corresponding interface chips or timing sequences.
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