The microcontroller is the core component of embedded systems, and circuits utilizing microcontrollers are much more complex due to programming requirements. However, circuits with microcontrollers are easier to modify and add new features to, which is why more and more electronic devices are now utilizing microcontrollers.
As a microcontroller R&D project, its minimum circuit working system consists of a power supply circuit, reset circuit, and clock circuit – these are the basic components of the circuit.
Power supply and reset circuits are generally easy for engineers to understand and design. However, the clock circuit is more difficult to design because different development projects have different functional requirements, making it challenging to achieve effective uniformity in design.
For example, one project may have strict cost requirements and simpler functions, while another may require serial communication with external circuit systems, with communication data that cannot be wrong.
In terms of the clock frequency circuit for the microcontroller, engineers design and select matching solutions based on different project requirements. There are two specific selection options available.
01. External Crystal Oscillator Scheme
The so-called external crystal oscillator scheme refers to connecting a crystal oscillator to the clock pins X1 and X2 of the microcontroller. As shown in the diagram below, this type of circuit is commonly used in early microcontroller circuits or in systems that require high clock accuracy. This is because internal clocks are limited in accuracy due to cost considerations in the microcontroller’s internal design space.
- Pros: The external crystal oscillator solution provides high clock frequency accuracy and stable performance. This makes it a suitable choice for projects with high data processing requirements, especially those that involve multiple circuit systems requiring information communication, such as projects that include USB or CAN communication.
- Cons: The use of an external crystal oscillator increases the cost of the bill of materials for the development project due to the additional components required. As a result, the cost is higher compared to other clock circuit options.
02. Internal Crystal Oscillator Scheme
The so-called internal crystal oscillator scheme refers to the microcontroller utilizing an internal integrated RC oscillator circuit to generate the clock frequency.
- Pros: The internal crystal oscillator solution eliminates the need for an external crystal oscillator, allowing engineers to effectively save on the cost of bill of materials (BOM) components for development.
- Cons: The clock frequency generated by the internal RC oscillator circuit has lower accuracy and larger errors compared to an external crystal oscillator. This can lead to errors in high-frequency communication data exchange.
This circuit does not require an external crystal oscillator or capacitors, making it particularly cost-effective for mass production. Therefore, it is widely adopted by cost-sensitive projects.
Next, let’s take a look at the general internal structure of the chip.
The system clock controller provides a clock source for the CPU and all peripheral systems of the microcontroller. There are three clock sources available for the system clock: internal high-precision 24MHz IRC, internal 32KHz IRC (with larger error), external crystal oscillator, or external clock signal. Users can enable and disable each clock source separately through the program, as well as use internal clock division to reduce power consumption.
When the microcontroller enters the power-down mode, the clock controller will turn off all clock sources.
03. In Conclusion
The use of microcontrollers in embedded systems has become increasingly popular due to their versatility and ease of modification. However, designing circuits with microcontrollers can be complex, especially when it comes to the clock circuit. In this article, we will discuss two clock circuit options available for microcontroller projects: the external crystal oscillator scheme and the internal crystal oscillator scheme.
The external crystal oscillator scheme provides high clock frequency accuracy and stable performance, making it a suitable choice for projects that involve multiple circuit systems requiring information communication, such as those with USB or CAN communication. However, this solution increases the cost of the bill of materials for the development project due to the additional components required.
On the other hand, the internal crystal oscillator solution utilizes an internal integrated RC oscillator circuit to generate the clock frequency, eliminating the need for an external crystal oscillator and reducing the cost of the bill of materials for development. However, the clock frequency generated by the internal RC oscillator circuit has lower accuracy and larger errors compared to an external crystal oscillator, which can lead to errors in high-frequency communication data exchange.
It is important to carefully consider the project requirements and budget when selecting a clock circuit option for a microcontroller project. The system clock controller provides a clock source for the CPU and all peripheral systems of the microcontroller, and users can enable and disable each clock source separately through the program, as well as use internal clock division to reduce power consumption.
04. Frequently Asked Questions about Optimizing Microcontroller Clock Circuits
Q1: What is a microcontroller and why is it important in embedded systems?
A1: A microcontroller is a core component of embedded systems that provides control and processing capabilities. It consists of a CPU, memory, and input/output peripherals on a single chip. Microcontrollers are important in embedded systems because they provide a convenient and cost-effective way to add intelligence and functionality to electronic devices.
Q2: What are the basic components of a microcontroller circuit?
A2: The basic components of a microcontroller circuit are the power supply circuit, reset circuit, and clock circuit. The power supply and reset circuits are generally easy to design, while the clock circuit is more complex because different projects have different requirements for clock frequency and accuracy.
Q3: What are the pros and cons of using an external crystal oscillator for clock generation in a microcontroller circuit?
A3: The pros of using an external crystal oscillator are that it provides high clock frequency accuracy and stable performance, making it suitable for projects with high data processing requirements. However, the cons are that it increases the cost of the bill of materials for the development project due to the additional components required.
Q4: What are the pros and cons of using an internal crystal oscillator for clock generation in a microcontroller circuit?
A4: The pros of using an internal crystal oscillator are that it eliminates the need for an external crystal oscillator, allowing engineers to effectively save on the cost of the bill of materials components for development. However, the cons are that the clock frequency generated by the internal RC oscillator circuit has lower accuracy and larger errors compared to an external crystal oscillator, which can lead to errors in high-frequency communication data exchange.
Q5: How does the clock controller of a microcontroller work?
A5: The clock controller of a microcontroller provides a clock source for the CPU and all peripheral systems of the microcontroller. It has three clock sources available: internal high-precision 24MHz IRC, internal 32KHz IRC (with larger error), external crystal oscillator, or external clock signal. Users can enable and disable each clock source separately through the program, as well as use internal clock division to reduce power consumption.
