MCU program RAM, ROM, Flash

8K flash has 8*1024 bytes. An instruction may have 1~4 machine codes, that is, 1~4 bytes. Among them, instructions with 1~2 machine codes are the most frequently used. So in this way, about 4000~8000 instructions can be written. General applications cannot write so many instructions. However, it may exceed the budget to store other data, such as Chinese characters and digital dot matrix codes. For the situation that it is really not enough, it is recommended that the host directly buy a large-capacity chip. Expanding flash is not very desirable, which increases the instability of the system, increases the area of ​​the board, and makes wiring difficult. If you really want to expand the capacity, there are many ways. Expand EEPROM (currently 256K~1M), or expand the flash memory based on SPI bus (mainstream 32M~128M). The drivers of these two buses are simple and easy to expand.

MCU FLASH is mainly used as program storage, which is to replace the previous ROM. The biggest advantage is that it reduces the cost of the chip and can be electrically erased. At present, the life of MCU FALSH on the market varies greatly, with erasure times ranging from 1,000 to 100,000, but the storage time can be guaranteed for 40 years. Pay attention when choosing. Some cheap MCUs do not use expensive EEPROM to integrate power-down data storage, but use FALSH. However, it should be noted that its life is up to 100,000 times, and it cannot be erased byte by byte. It should be noted that whether its life meets the requirements in the occasion of use.

RAM is a data storage device, similar to the memory in a computer. It is mainly used to store process data during program operation. After power failure, the previous data will be lost, so the program needs to be initialized when powered on, otherwise the data after power on will be a random number, which may cause the program to crash.

ROM is the program memory. The data will not be lost after power failure, but the data will not change during the program running. The ROM of the early microcontrollers has been replaced by the current FLASH memory because of the trouble of erasing and modifying, the high price or the inability to modify the data of the cheap OTP type. Because FLASH is easy to erase and write, some microcontrollers now support online internal programming. The content of FALSH can be modified through a specific program execution method, and the program memory can be modified online. This does not conflict with the above-mentioned content of the program memory cannot be changed during operation, because when the program is running normally, its content will not change and it only works in a read-only state.