MITSUBISHI HEAVY INDUSTRIES,LTD.

Making Extensive of Renesas Microcomputers in Broad Range of Air Conditioners

The company first started using M16C family microcomputers six years ago. A major factor in the selection process was the extremely diverse range of versions of these 16-bit microcomputers. "At the time, there was no other range of 16-bit microcomputers as extensive as the M16C family," Mr. Otake said.

A primary design issue favoring the devices in the M16C family was their extremely high tolerance for noise. The signals to the microcomputer from the multiple sensors used in air conditioning control are degraded by noise from sources such as the power supply and mechanical vibration. The microcomputers used prior to the M16C family had poor noise tolerance. To make those devices work reliably, the engineers at MITSUBISHI HEAVY INDUSTRIES had to add to the peripheral functions various circuits for improving noise performance, and those extra circuits increased the cost of the product.

After conducting evaluation tests, the engineers concluded that the Renesas M16C microcomputers have two to five times better noise tolerance than the chips previously used. "By switching to the M16C devices, there has been a big reduction in the volume of work associated with peripheral circuit design. Our air conditioner designers are very grateful for that improvement," said Mr. Otake. The high tolerance for noise is one of the reasons why the company has chosen to continue using the M16C family.

Another factor in favor of the M16C devices is that the packages have pin layouts that are compatible between each device series. This eliminates the need to make design changes in components such as printed circuit boards and peripheral hardware when developing a range of air conditioner models. It also provides other benefits, such as allowing the reuse of existing resources and the sharing of common control program software.

MITSUBISHI HEAVY INDUSTRIES is strong supplier of the "multi air conditioners" used in offices and other buildings. Those products combine a large number of indoor units with a single outdoor unit. "The algorithms used for air conditioning control in multi air conditioners are particularly complex and contain large amounts of code. The 384Kbyte internal ROM capacity of the M16C microcomputers is important because it can accommodate our code size."

Of course, Renesas also offers microcomputers with on-chip flash memory, as well versions with ROM. Commenting on this, Mr. Otake said, "As air conditioners become more diverse and motor control becomes more complex, the adoption of flash memory ― along with high-performance, high-capacity ROM microcomputers with additional new functions ― is becoming more and more essential as a means of shortening development times and reducing costs."

The company also uses SuperH family (SH-2 series) microcomputers for inverter control in the outdoor units of its package air conditioners. Moreover, it has already developed room air conditioners that use a single SuperH family (SH-2 series) device to implement both air conditioning control and inverter control. Renesas will continue to support product development in this market by supplying a wide range of products for different applications and functions.

Web site of the Air Conditioning and Refrigeration Systems Division of MITSUBISHI HEAVY INDUSTRIES,LTD.
http://www.mhi.co.jp/en/aircon/index.html