The memory of the 51 MCU can be divided into program memory and data memory by functional division. Generally speaking, the storage space of the MCU memory is capable of expanding the storage space, but how to expand it needs to be selected according to different memory types. This article will explain this problem for everyone.
When accessing the storage space, two pointer variables are required, which are DPTR and PC. Among them pc is the program counter, pointing to the address of the next instruction to be executed, DPTR is the data pointer register, the length of these two variables are 16 bits, which is determined by the internal structure of 51 microcontroller, can not be changed. So the addressing capabilities of these two pointers are 64K. In this way, both types of memory have an expansion capability of 64K. However, if you actually expand the memory, you can find that the program memory's expansion capability is not 64K.
Why is this like this? This has to start from the addressing of the storage space of 51 single-chip microcomputer. Here is a brief description, specifically the textbook. Simply put, the internal program memory and the external program memory are addressed together, they occupy a part of the 64K address, so the external address space should be subtracted from the external expansion, of course, less than 64K. The data memory is internally and externally addressed separately, and the internal and external data memory are accessed by different instructions, so there is no need to worry that the MCU will confuse the internal and external data memory, so the external data memory expansion capability is 64K.
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