Experience and summary of register operation methods

Working with the STM32 function library has been very convenient, but few microcontrollers come with such libraries. In most cases, you have to interact directly with the registers, so it's important not to ignore register operations.

When working with registers, the order of bits matters. A small mistake in the sequence can lead to unexpected results. While this isn't a perfect summary, the method for manipulating registers is quite standard.

Before diving into register operations, it's essential to understand the difference between logical operators (!, &&, ||) and bitwise operators (<<, >>, ~, |, ^, &). Register manipulation relies on bitwise operators, while logical operators are typically used for decision-making in programs.

For example, consider an 8-bit register located at address 0xF0:

#define REG 0xFF

1) Setting or clearing individual bits:

(1) Set bit 5 of register REG to "1":
REG |= (1 << 5);

(2) Clear bit 5 of register REG:
REG &= ~(1 << 5);

(3) Set bits 3 and 5 of register REG to "1":
REG |= (1 << 5) | (1 << 3);

(4) Clear bits 3 and 5 of register REG:
REG &= ~((1 << 5) | (1 << 3));

The general rule is: use the bitwise OR operator "|" to set bits to 1, and the bitwise AND operator "&" to clear bits to 0.

2) Direct assignment:

(1) Set bits 1, 2, 3, 5, and 7 of register REG to "1":
REG = 0x5E;
(This sets the register to 1010 1110, commonly used during initialization.)

(2) Set bits 1, 3, 5, and 7 to "1", and bits 0, 2 to "0":
U8 temp;
temp = REG;
temp &= ~0x01; // Clear bit 0
temp |= (1 << 1);
temp &= ~(1 << 2);
temp |= (1 << 3);
temp |= (1 << 5);
temp |= (1 << 7);
REG = temp;

Understanding how to manipulate bits is crucial when working with embedded systems. It allows for precise control over hardware peripherals and ensures that your code behaves as expected.