Experience and summary of register operation methods

Working with the STM32 function library has been quite convenient, but it's worth noting that not many microcontrollers come with such libraries. In most cases, you have to interact directly with the registers, so it's important not to neglect understanding how register operations work.

Register manipulation often involves paying attention to the order of bits, as incorrect handling can lead to unexpected results. While this isn't a comprehensive guide, the method for working with registers is pretty standard and follows specific patterns.

Before diving into register operations, it's essential to understand the difference between logical operators (!, &&, ||) and bitwise operators (<<, >>, ~, |, ^, &). Register operations typically use bitwise operators, while logical operators are more commonly used in program logic and conditional checks.

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 the register to "1":
REG |= (1 << 5);

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

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

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

The key takeaway is: To set a bit to 1, use the bitwise OR operator "|". To clear a bit, use the bitwise AND operator "&" after inverting the mask with "~".

2) Direct assignment

(1) Set bits 1, 2, 3, 5, and 7 to "1":
REG = 0x5E;

(This means the binary value is 01011110, which is often used during initialization.)

(2) Set bits 1, 3, 5, and 7 to "1", and bits 0 and 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;

This approach gives you fine-grained control over each bit, making it ideal when you need precise configuration of the register.

Understanding these operations helps in writing efficient and reliable embedded code. Whether you're using a function library or working directly with registers, having a solid grasp of bitwise operations is essential for any embedded systems developer.