The amount and sophistication of electronics in cars is increasing at a very fast pace, driven primarily by two goals: to increase the functionality and the safety of the vehicle. Implementing these new functions in electronics is a cost-effective way to achieve these goals with a level of reliability that consumers have come to expect. There are a variety of subsystems in the car, such as the chassis electronics, driver information electronics and body electronics. Body electronics subsystems are responsible for functions such as seat positions, interior lighting and wiper control. Intelligent design allows body control modules (BCMs) to drive loads more efficiently and reliably.

The BCM is fast becoming one of the most important modules in a vehicle. The purpose of the BCM is to control common “body” functions that don't require a dedicated controller, such as functions to control windows, mirrors, door locks and lights or RF receiver functions that receive information from key fobs and tire monitors. The BCM can also act as the gateway to transmit data between different modules on the various network buses. Because of its connection to multiple vehicle buses, the BCM is an ideal place to add new functionality to a vehicle. When vehicle architects want to implement a new function, but don't have the time, space or budget to add a new module, they can often add the software to the BCM and take advantage of its networking capabilities to implement the feature.

While BCM requirements obviously vary from vehicle to vehicle, the trend for carmakers is to develop a single module that covers multiple carlines. By doing this, carmakers reduce their development and maintenance costs, which offset the slightly higher module cost. The single module can then be deployed more quickly across multiple platforms with minimal configuration done on the actual vehicle, reducing the complete time to market.

The operation of a BCM can be divided into two broad categories: the control section that includes microcontrollers (MCUs), sensor inputs and in-vehicle networking, and the power section that includes the devices capable of supplying the high-power signals to drive the various loads. Designing the power section requires an understanding of the different types of loads that are used in body electronics. For example, LEDs are quickly replacing incandescent lights in both interior and exterior lighting due to their low power, superior robustness and reliability. Electric motors are being used for mechanical functions to raise and lower windows, change seat positions and adjust mirrors. Resistive elements are used in heat seating and rear-window defrosters. The challenge exists in merging the control and power section into a single module. When BCM designers start a new design, they must consider all possible components that can be used for the control and power sections. Then they must determine the combination that best meets the requirements, while taking into consideration all system constraints. Some of the major constraints designers have to be concerned with when choosing the right combination of parts are power budgets, thermal behaviors, robustness and, of course, cost. For example, power sections have traditionally been implemented exclusively using power relays, but recent designs have demonstrated a migration trend toward solid-state solutions. Solid-state electronics can offer more robust solutions that can lead to lower overall costs. In addition, by combining these solid-state devices with intelligent digital controllers, designers can introduce diagnostics and fault protections that haven't been possible before. Ultimately, the designer's goal is to create a cost-effective BCM that completely meets the application requirements and provides high reliability to meet stringent automotive standards.

A general block diagram of a BCM module (Figure 1) shows the module connected to sensor inputs, and also to the power section. The advantage a microcontroller brings is the ability to partition the control problem between the hardware peripherals and the software routines. This gives the module designer much more flexibility than if the control were implemented in hardware. Using an MCU not only adds more flexibility and function to the system, it can also increase the robustness by allowing for diagnostics within the system, even to the extent of having a self-test capability.

When implementing the control portion of the body module, the most critical decision is selecting an MCU with the right peripherals that can meet the performance and cost targets of the application. NEC Electronics, for instance, has recognized the trends in body electronics and has developed solutions such as the V850ES/Fx3 MCUs, which are based on the company's V850 32-bit CPU core and optimized for body automotive applications. Developed for embedded systems, the real-time performance of the V850 core delivers high-performance processing capability, fast interrupt response time and efficient transfer of data. The core also includes a dedicated interrupt controller with individual vectors for each interrupt source, enabling fast servicing of requests. The on-chip direct memory access (DMA) unit has access to memory and system buses, allowing for autonomous transfer of data without CPU intervention.

The V850ES/Fx3 MCUs integrate a number of advanced peripherals necessary for body modules in particular (Figure 2). For instance, timers are critical to body applications as they are used for scheduling tasks, capturing external signals like RF pulses and, most important, generating pulse-width modulated (PWM) signals for controlling loads such as interior LEDs. The V850ES/Fx3 MCUs offer numerous timer macros with programmable flexibility to run in various modes, as well as capabilities to synchronize timers to increase PWM capabilities. To support the growing networking requirements of OEMs, the lineup incorporates up to five controller area network (CAN) channels, each with individual message buffers and mask registers that filter messages without CPU intervention. For the slower-speed, local interconnect network (LIN) applications, the MCUs support up to eight LIN channels with an additional multi-LIN-master (MLM) unit that handles the LIN protocol in hardware, removing the overhead from the CPU. For analog signals, there are up to 40 channels of analog-to-digital converters with features including pin diagnostics, automatic discharge, and flexible trigger sources.

In addition to the requirements for intelligent on-chip peripherals, the overwhelming trend in embedded automotive electronics is to use flash memory. For instance, the V850ES/Fx3 MCUs offer flash memory for code in sizes ranging from 64 kB to as much as 1 MB, as well as separate on-chip memory that can be used as data memory for high-endurance data.

One of the most demanding constraints for MCUs in body electronics is the need to continue running while the vehicle is turned off. In this situation, the MCU has to support a standby mode that provides the necessary functionality at the right power consumption level. The V850ES/Fx3 MCUs feature NEC Electronics' MF2 embedded flash process technology for low-power modes that enable the MCU to run only the necessary peripherals, such as internal clocks and periodic timers required by the system, while consuming as little as 10 to 15 microamperes of power to meet even the toughest power budget. Combining the benefits of high-density flash memory with low-leakage logic enables the overall MCU to exceed in performance-to-cost ratio while also managing to consume little power.