Toyota Motor Corporation Headquarters: 1 Toyota-cho, Toyota City, Aichi Prefecture Web site URL: http://toyota.jp/

Kan Ohtsuka General Manager Vehicle Electronics Engineer Div. Toyota Development Center 1 Product Development Group Toyota Motor Corporation

Microcomputers are used in vehicles to control the core functions of driving, turning, and stopping. They're also essential components for delivering greater added value in areas such as safety, confidence, and comfort. Toyota Motor Corporation is the world's second largest automotive manufacturer, with total (consolidated) sales of 6,719,000 vehicles (March quarter, 2004), and its requirements for flash microcomputers are growing rapidly. Renesas F-ZTAT microcomputers, having gained a strong reputation through features such as excellent noise immunity and low power consumption, are being used increasingly at Toyota because they deliver a variety of important advantages.

Toyota's CROWN MAJESTA "Aero Version." Top-end models such as this one use about 100 microcomputers.

Edge: The use of electronics in automobiles just keeps on growing doesn't it?

Ohtsuka: That's right. The increasing use of electronics is happening not just in the driving systems such as engine, transmission, and chassis control, but also in many other areas, including safety systems, body systems, and information systems. Even a typical small car will have several tens of electronic control units (ECUs) and a top-end model will have more than sixty.

Program sizes are also expanding rapidly, with some reaching as many as 200,000 lines of code. When programs get that large, the issues of software productivity and how to ensure software quality become serious problems.

Edge: Does the use of electronics play a major role in providing the advanced functions demanded in top-end vehicles?

Ohtsuka: For example, high-end models have features that we call "hospitality functions." These are functions that give the impression of a high-end model, such as the indicator lights next to the dials turning on one after another instead of all at once, and illuminating automatically when someone with an intelligent key approaches the vehicle. Electronics are required to implement these.

In other functions, also, electronics based on microcomputers have taken an important role in providing a range of different added values to the vehicle.

Edge: As the number of microcomputers used in vehicles increases, I understand that the requirements for flash microcomputers in particular have grown.

Ohtsuka: Although mask-type microcomputers are still the mainstay, cars have now entered an era of shorter development times, and at times the software development cycle has not meshed with the overall development cycle. As the development cycle for automobiles gets shorter, the specifications for the software to be written to mask ROM must also be fixed at an earlier time. However, due to the rapid increase in program size, the reality is that it is becoming more difficult to finalize the specifications in less time.

For this reason, what we are now also doing is using flash microcomputers during development both to provide lead time and to allow programs to be updated, and then switching over to mask ROM microcomputers once the software has been completely finalized.

Edge: The ability to switch over to mask-type microcomputers after development is complete is one of the advantages of flash microcomputers, but we understand you also see advantages in continuing to use flash microcomputers right up to the production stage.

Ohtsuka: The main reason for switching to mask-type microcomputers is, of course, their lower cost. My own opinion, however, is that flash microcomputers have other cost-advantages that are not apparent in the microcomputer's unit price. For example, if mask microcomputers are maintained as stocks of consumables, there is obviously an associated management cost. If we were to use flash microcomputers exclusively, though, we would be able to reduce the number of parts we use. Given the increased number of ECUs used in modern cars, the benefits of reducing the number of parts would be significant.

Edge: If vehicles are using several tens or more of ECUs each, the amount of work associated with ECU maintenance must be becoming a problem.

Ohtsuka: That's right. Because of the need to provide more cabin space in modern cars, it is becoming difficult to provide adequate space for maintenance so that installed ECUs can be removed. Also, production techniques such as in-panel assembly are improving. But if the panel is removed to replace the ECU and then everything has to be put back together again, the process involves a lot of work and has an effect on quality.

As a result, there is a growing need to adopt a different approach by using flash microcomputers that support network-based software upgrading from outside the vehicle via the vehicle LAN.

Edge: In the case of learning control systems, is the ability to store learning data on the microcomputer itself also a major advantage?

Ohtsuka: Certainly there are ECUs that perform control functions based on learning data. Although the battery normally protects the data, there are times when the information must be repaired, particularly if users change the battery themselves. Although the manual for the vehicle explains how to repair the data, we cannot expect all users to be able to perform such procedures.

If the learning data can instead be written to and stored on a flash microcomputer, the data are maintained even when power is interrupted. This eliminates the need to repair the data after changing the battery and makes the vehicle easier to work on for both the user and the technician at the garage.

Edge: You use a large number of Renesas microcomputers. Can you tell us the reasons why?

Ohtsuka: We are impressed by Renesas flash microcomputers because of their characteristics such as noise immunity and low power consumption in particular.

Cars have a large noise source: the engine. Therefore, microcomputers that have strong noise characteristics in terms of both EMI and EMC are required. Although ECU circuits and enclosures incorporate anti-noise measures, the microcomputer itself still has to have good immunity to noise.

Also, the growing number of ECUs we are using in our vehicles are powered entirely by the battery. Battery capacity is designed to provide a certain amount of power for maintaining functions and starting the engine, while the generator has to provide adequate power when the car is running. However, more and more in-vehicle functions, such as the immobilizer, must continue to operate even when the ignition key is completely turned off. Accordingly, the use of electronic devices with low power consumption is an essential part of minimizing the amount of standby current drawn by such functions, and reducing the power consumption of microcomputers is of particular concern.

Edge: Thank you for taking the time to talk with us today.