Stm32-fsmc extended memory SRAM

FSMC Extended memory SRAM

Introduction to common memory

Type of memory

Type of memory ： Memory is an important part of computer structure . Memory is a component used to store program code and data , Only with memory can a computer have memory function

RAM Memory

RAM：RAM yes “Random Access Memory” Abbreviation , Random access memory . So-called “ Random access ”, Refers to when a message in memory is read or written , The time required is independent of the location of this information . The origin of this word is that early computers used magnetic drums as memory , The magnetic drum is a sequential read-write device , and RAM You can read the data of any address inside it , The time is the same , Hence the name .
Actually now RAM It has been specially used to refer to volatile semiconductor memory as computer memory .
according to RAM The storage mechanism of , It is also divided into dynamic random access memory DRAM(Dynamic RAM) And static random access memory SRAM(Static RAM) Two kinds of .

SRAM The memory of

SRAM Storage unit structure

​ Static random access memory SRAM The data is stored in a latch unit , See the picture . This circuit structure does not need to refresh and charge regularly , Can stay in shape ( Of course , If there is a power failure , Data will still be lost ), So this kind of memory is called “ static state (Static)”RAM.

similarly ,SRAM It is also divided into synchronization according to its communication mode SRAM And asynchronous SRAM, relatively speaking , asynchronous SRAM Used more .

DDR SDRAM

In order to further improve SDRAM Communication speed of , People designed DDR SDRAM (Double DataRate SDRAM) Memory .DDR SDRAM The rising and falling edges of the clock each represent a data , That is to say 1 A clock cycle can represent 2 data , With the same clock frequency , Double the speed

DRAM The memory of

DRAM Storage unit structure ：

Dynamic RAM DRAM(Dynamic RAM)

Dynamic refresh

Dynamic RAM DRAM The storage unit of represents data by the charge of capacitance , An electric charge represents 1, No charge represents 0,, representative 1 The capacitor will discharge , representative 0 The capacitor absorbs the charge , therefore
It requires periodic refresh operations , This is it. “ dynamic (Dynamic)”

Synchronous and asynchronous DRAM：

​ according to DRAM The way of communication , It is also divided into synchronous and asynchronous , These two methods are distinguished according to whether the clock signal needs to be used in communication . Because the communication speed using clock synchronization is faster , So synchronization DRAM More widely used , such DRAM go by the name of SDRAM(Synchronous DRAM). common DRAN Mostly SDRAM

DRAM And SRAM Applications of

DRAM and SRAM Comparison of characteristics ：

SRAM It is usually used only for CPU Internal cache (Cache), External extended memory is generally used DRAM.

Nonvolatile memory

There are many kinds of nonvolatile memory , Semiconductors are ROM and FLASH, Others include CDs 、 Floppy disk and mechanical hard disk .
ROM Memory
ROM yes “Read Only Memory” Abbreviation , Read only memory . Because of the development of Technology , Later, it was designed to write data easily ROM, And this “Read Only Memory” The name of has been used , Now it is generally used to refer to nonvolatile semiconductor memory , Including the following FLASH Memory , Some people also put it under ROM Class inside .

FLASH Memory

FLASH Memory is also called flash memory , It is also a rewritable storage , Some books will put FLASH Memory is called FLASH ROM, But its capacity is generally larger than EEPROM Much more , And when erased , Usually in multiple bytes .
Depending on the circuit of the storage unit ,FLASH Memory is divided into NOR FLASH and NAND FLASH

SRAM Control principle

SRAM brief introduction

STM32 And SRAM：
STM32 The controller chip has a certain size SRAM And FLASH As memory and program storage space , But when the program is large , When memory and program space are insufficient , It needs to be in STM32 The external expansion memory of the chip .STM32F407 Series chips can be extended externally SRAM Used as memory .
to STM32 The chip expands memory and gives PC The principle of expanding memory is the same , It's just PC It is generally extended in the form of memory module , And the memory module is essentially composed of multiple memory particles ( namely SDRAM chip ) A general standard module , and STM32 When expanding , Direct and SRAM Chip connection .

SRAM The signal line

IS61LV25616SRAM

SARM Internal block diagram analysis

SRAM The control of is relatively simple , As long as the control signal line enables access , from I/O Port data line writes or reads data .