Experience and summary of register operation methods

The STM32 function library that has been in contact for a while is very convenient to use, but few processors have function libraries. In most cases, you have to operate the registers yourself, so you should not alienate the operation of the registers.

The operation of the register sometimes takes into account the different order of its different bits, because this may not achieve the expected effect, this is not a good summary, but the method of register operation is fixed.

Before that, we must first understand the difference between the logical operator (! && ||) and the bitwise operator (<< >> ~ | ^&). The operation of the register uses the bit operator, which is generally used for logical operators. Used in the judgment logic in the program.

For example, define an 8-bit register (0xf0 is the address of the register):

#define REG 0xFF

1) Assign a single bit

(1) Set the 5th position of the register REG to "1"

REG |= (1 << 5);

(2) Clear bit 5 of register REG

REG &= ~(1 << 5);

(3) Set the 3rd and 5th positions of the register REG to "1"

REG |= (1 << 5) | (1 << 3);

(4) Clear bits 3 and 5 of register REG

REG &= ~( (1 << 5) | (1 << 3) );

The paragraph is summarized as follows:

Set a position to 1 and shift the bit to use the bitwise operation "|"

After a position 0 is shifted, the bitwise operation "&" is used.

2) Direct assignment

(1) Position 1, 2, 3, 5, 7 of register REG "1"

REG = 0x5E;

(ie assign the register REG1 to 1010 1110, this method is mostly used in the initialization)

(2) Position 1, 3, 5, and 7 of register REG are set to "1", and 0, 2 are set to "0".

U8 temp;

Tmep = REG;

Temp &= ~0x01; //Equivalent to temp &=~(1<<0) Clear bit 0

Temp |= (1 << 1);

Temp &= ~(1 << 2);

Temp |= (1 << 3);

Temp |= (1 << 5);

Temp |= (1 << 7);

REG = temp;