MCU sfr and sbit keywords

The usage of bit is similar to sfr, except that sbit is a bit operation, which is used to assign a specific bit in an sfr to a variable, so that the program can use the variable to clear or set the bit.

sfr is used to assign a special function register of a microcontroller to a variable, so that the variable can refer to the register in subsequent programs.

The usage of sbit is similar to that of sfr, except that sbit is a bit operation, which is used to assign a specific bit in an sfr to a variable, so that the program can use the variable to clear or set the bit.

The special function register layout of STC series microcontrollers is as follows:

After looking at so many special function registers in Figure 1, you may have some confusion. We use sfr P0 = 0×80 to represent P0 and sfr SP = 0×81 to represent SP. There is no ambiguity. What is confusing is: if sbit P0_1 = 0×81 is used to represent the first bit of port P0, then what should I do if I want to represent the 0th bit of the SP register? If it is also defined as sbit SP_0 = 0×81, then there will be obvious ambiguity and the compiler cannot understand it. In fact, this problem does not exist. As can be seen from Figure 1, SFR can be divided into two areas: bit-addressable area and non-bit-addressable area. The register address of the bit-addressable area can be divided by 8, while the register address of the non-bit-addressable area does not meet this requirement. Therefore, sbit SP_0 = 0×81 in the example is invalid for the SP register and should be written as sfr SP=0x81.

For example: sbit P1^1=0x81;sfr SP=0x81;

Although they both refer to the same address 0×81, the compiler has completely different meanings. The former is a byte address because of the sfr keyword, while the latter is a bit address because of the sbit keyword, indicating a bit.