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This article mainly introduces what STM32 bit segment means. The introduction in this article is very detailed and has certain reference value. Interested friends must read it!

1 defines

First of all, we need to clarify the following three nouns: lower segment, bit band and alias area

Bits: Names used in STM32 User Reference Manual

Bit bands: CortexM3 reference manual used

alias area: an area on the address bus used for bit access to addresses,

Therefore, bit segment and bit band are the same meaning, and they are different names in different manuals.

From the above noun explanation, it is known that the bit band function is not unique to STM32, but is a function of CortexM3 (CortexM4 also has such a function). MCS51 has bit operation, with one bit as the data object operation, MCS51 can simply set the second bit of port P1 independently: P1.2=0;P1.2=1 ; thus setting the third pin of port P1 (bit2) to 0 and 1. The most important thing about STM32's bit segment and bit band alias area is to realize such functions.

2 bit band operation 2.1 range

Bit bands are scoped and not supported by all address spaces of CortexM3. In CM3, bitbands are implemented in two regions. One of these is the lowest 1MB range of SRAM area, and the second is the lowest 1MB range of on-chip and off-chip areas. In addition to the fact that the addresses in these two areas can be used like normal RAM, they also have their own "bit-band alias areas," which inflate each bit into a 32-bit word. When you access these words through the bit-band alias area, you can access the original bits.

The two memory areas that support bit-banding operations range from:

0x2000_0000‐0x200F_FFFF (lowest 1MB area in SRAM area)

0x4000_0000‐0x400F_FFFF (minimum 1MB in on-chip peripheral area)

2.2 bit-band operation

For a certain bit in SRAM bit strip area, the address of byte where the bit is located is A, and the bit number is n (0

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