Advanced car dashboard and body control design essentials

Today's cars have entered an era of intelligent and environmentally friendly design. In terms of intelligence, digital electronics technology is used to enhance the safety and comfort of automobiles, and environmental protection is achieved through the design of hybrid electric vehicles and electric vehicles. The goal of carbon. As a result, today's cars are becoming more and more electronic. From infotainment, bodywork, safety to powertrain, the use of electronic components for sensing and manipulation has penetrated into every corner of the car.

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In the various systems of automotive electronics, it is often necessary to use a microcontroller (MCU) as the core of operational control, and the dependence of the car on the electronic system also stimulates the rapid growth of the automotive microcontroller market. The vehicle's microcontrollers cover low, medium and high-end product grades such as 8-bit, 16-bit and 32-bit, each with its own suitable application system, which is roughly as follows:

8-bit MCU: Mainly used in various subsystems of the car body, including fan control, air conditioning control, wiper, sunroof, window lift, low-end instrument panel, junction box, seat control, door control module, etc. control function.

16-bit MCU: Mainly used in powertrain systems such as engine control, gear and clutch control, and electronic turbine systems; also suitable for chassis mechanisms such as suspension systems, electronic power steering, torque dispersion control, and Electronic pump, electronic brakes, etc.

32-bit MCUs: Main applications include dashboard control, body control, telematics, engine control, and emerging intelligent and real-time security systems and power systems such as Pre-crash, adaptive Safety functions such as cruise control (ACC), driver assistance system, electronic stability program, and complex X-by-wire transmission functions.

Common interface for automotive MCU: CAN & LIN

With the ever-increasing demands of today's automotive applications, the systems that need to be integrated are becoming more and more complex, making the demand for high-end 32-bit MCUs in automotive electronic systems increasing. Such MCUs for vehicles are often placed in a high-heat, dusty, shock, and electronically disturbed operating environment, so the tolerance requirements are much higher than general-purpose MCUs. In addition, in automotive applications, automotive MCUs must be connected to multiple automotive electronic control units (ECUs), the most common of which are CAN and LIN.

CAN is divided into high-speed CAN and low-speed CAN. The transmission rate of high-speed CAN can reach 1 Mbps. It is suitable for applications that emphasize real-time response such as ABS and EMS. Low-speed CAN can reach 125 Kbps, which is suitable for lower-speed car body parts control. In addition, the CAN controller can be divided into the old 1.x, the standard 2.0A and the extended 2.0B. The newer specifications are naturally better, and the 2.0B can be divided into passive and Active type.

LIN is a lower speed and lower cost communication scheme than CAN. It adopts the concept of one master node and multiple slave nodes (up to 16 nodes), up to 20 kbps data transmission rate, and the length of bus cable can be extended up to 40 meters. It is ideal for Climate Control, Mirrors, Door Modules, Seats, Smart Switches, Low-cost Sensors A distributed communication solution that is simpler than a simple system.

The next generation of MCU technology for instrument panel control and body control will be introduced, and Fujitsu's new MB91770 series and MB91725 series of new microcontrollers will be used as design reference. Please refer to (Figure 1).

Figure 1 Dashboard control and body control MCU application in the car (take MB91770 series and MB91725 series as an example)

Automotive dashboard and body control design essentials

The dashboard of the car provides a variety of real-time visual information for driving. This information is an important reference for assisting decision making and must be communicated to the driver quickly and accurately. In addition, the air conditioning and body control module (BCM) system in the car is responsible for providing a comfortable ride environment for driving and passengers. Among them, the air conditioning system performs optimal control to quickly reduce the temperature inside the car to a relatively comfortable level, and maintains a comfortable interior temperature based on information from various sensors. The BCM system can centrally control multiple ECUs such as doors, seats and combination switches.

MCUs, whether dashboard control or body control, must provide higher processing performance, the ability to handle large numbers of network nodes, interface functions that support multiple peripheral connections, expandable board layout range, and advanced memory architecture. And a more convenient development environment. These design requirements are analyzed as follows:

High processing performance:

To improve processing performance, MCUs must take the FR81S CPU core of Fujitsu's next-generation MCU from its core and software and hardware system architecture as an example. Its working performance reaches 1.3MIPS/MHz, which is 30% higher than the previous generation FR60 core. Performance; with built-in single-precision floating-point arithmetic unit (FPU), it can meet the requirements of image processing systems and systems that require floating-point operation (such as brake control). In addition, hardware FPU support simplifies software programs and improves computing performance.

2. A large number of network node processing capabilities:

There are a large number of built-in ECUs in the CAN network in today's cars. Their size has been increasing with the number of nodes, so the car MCU must support more message buffers. The previous generation of 32-bit CAN microcontrollers can provide up to 32 built-in message buffers, but now it is not enough. With the new generation of Fujitsu MCUs, it can support up to 64 built-in message buffers, and support CAN 2.0A/B specification and high transmission rate of 1Mbps.

3. Broad interface support capabilities:

The periphery of the car MCU connection is quite diverse, and the connected interface may be UART, frequency synchronous serial, LIN-UART and I2C, so it must have flexible interface connection capability. In order to meet this demand, Fujitsu uses the built-in multi-function serial interface as a serial communication interface, and switches the above various interfaces through software to flexibly support the communication specifications of external components and improve the freedom of system design. The new family of MCUs also offers six channels of LIN-UART for communication with more control units; the MB91725 series is easier to integrate with various functions due to multiple channels and A/D converters with timer function. . Please refer to (Figure 2).

Figure 2: Using the serial interface to achieve flexible communication interface function integration

Expandable board layout range features:

Since the layout design of the vehicle circuit board system is quite diverse, the vehicle MCU must be able to meet the needs of these designs. Some possible practices include configuring an independent Power Supply for the external bus interface terminals so that no level shifters need to be installed on the ECU board. This external bus interface terminal has a wide power supply range (eg, covering 3.0V to 5.5V), and can be flexibly connected to the unit memory or image ASIC.

Another way is to let the MCU have the built-in I/O redistribution function, and the I/O port can be changed through software settings. In this way, the designer can be more flexibly connected to a specific periphery, thereby greatly increasing the degree of freedom in board layout.

5. Advanced memory architecture:

In order to improve the flexibility of work processing, embedded memory (Flash) is often built into the system of today's automotive microcontrollers. In the past, only Flash was used for program storage, and Flash for data was added to the architecture of the new generation MCU. This architecture not only improves data write speed, but also reduces the board area by eliminating the need for E2PROM. In addition, storing data and programs in the flash memory of the microcontroller also helps prevent information leakage.

6. More convenient development environment:

General products must use the ICE main unit and verification evaluation chip for system verification. In order to reduce the complexity of verification, we provide on-chip debugging mode for next-generation MCU products. It features a single-wire debug interface for automotive evaluation or compliance testing, and enables communication between small ICE main units and target boards up to 10 meters with universal coaxial cable. This simplifies vehicle evaluation that is difficult to achieve in routine.

Figure 3 uses the on-chip debugging to achieve vehicle evaluation


in conclusion

The electronic system in a car is becoming more and more complicated, and the dependence on the car MCU is getting deeper and deeper. For the design of automobile dashboards and body controls, it is necessary to provide accurate and quick auxiliary information for driving, as well as to facilitate comfortable driving space. Therefore, related MCUs must also meet higher performance and more flexible design requirements in order to be functionally applicable. Development brings help.

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