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Volume 56 (Apr 26, 2006)
NEC Electronics' Microcontrollers: Supporting the Evolution of Car Audio from Behind the Scenes (1/2)
< Part 1 >
Tracing the history of microcontrollers and their role in the evolution of car audio: Development of the world's first single-chip digital tuning system
You cannot talk about microcontrollers for car audio use without first discussing digital tuning systems (DTS), which are now commonly used as audio tuners. About 30 years ago, in the mid 1970s, NEC Electronics (then NEC) became the first in the world to develop a microcontroller specifically for DTS use. We asked Kazuhide Kawata, who was involved in the development of this microcontroller, about the circumstances at that time.
- Please begin by telling us the background behind the development of the digital tuning system.
Thirty years ago, the only car audio product available was the car radio. At the time, car radio tuners had tuning circuits that were set up for each radio station's frequency and these circuits were mechanically selected using switches. To select a radio station, you push the button for that station. However since only one station was allotted to each button, the number of radio stations that could be selected was very limited. Furthermore, because there was a tuning circuit for each radio station, car radio systems were rather large in size.
That's where NEC Electronics came in. At the time, we had developed a single-chip LSI that incorporated a PLL frequency synthesizer, which had up until then been used in radios for aviation use, etc. This digital tuning system LSI—from the µPD1700 series of 4-bit microcontrollers—boasted numerous advantages. Just as with mechanical systems, there was no need to designate a tuning circuit for each radio station, PLL control enabled stable reception, and—as has become commonplace today—a receiving frequency could be read directly.
- Yet your customers were not very receptive at first, were they?
We began mass production at the end of the 1970s, but at first, the µPD1700 series was not very well accepted in the car radio market. This was because its cost was five times more expensive than that of a mechanical system. And since microcontrollers at that time were thought to be a noise generator, the notion of using them in a car radio was simply ridiculous to many. This was only natural because the digital noise emitted by microcontrollers affects a radio's receiving circuit. To eliminate noise, we drew on our wealth of know-how. We also established oscillator frequencies to prevent harmonic noise emitted by microcontrollers from affecting frequency bands of broadcasting stations around the world, and also altered the design so that the PLL built into the LSI would not be influenced by noise coming from the microcontroller. It was also necessary to develop noise countermeasures to combat exogenous noise since this type of noise greatly affects car radios. We also made changes to the software to prevent the microcontroller from performing unpredictable operations due to exogenous noise.
- What was the catalyst behind the sudden increase in popularity of the µPD1700 series?
It was around that time that we were approached by a rather unexpected customer—a home audio product manufacturer. The µPD1700 series was beginning to garner a great deal of attention thanks to its stable reception performance. We then began to hear from the once skeptical manufacturers of car audio products. The fact that we had the technological strength needed to develop microcontroller software that met the needs of our customers, and used that as a base for offering total solutions for the development of software for car radios as a whole, greatly contributed to the use of this series in car radios. This is how we were able to achieve monthly production levels exceeding one million units for the µPD1700 series during the first half of the 1980s, five to six years after sales of the series began.
- And ever since then you have developed one new product after another and have taken the lead in car radios, haven't you?
We then went on to develop and add the µPD1708, which incorporated an FM band (over 100 MHz) prescaler (a component that divides frequencies) into a chip, to the µPD1700 series. The µPD1708 was a product with excellent cost performance and therefore became the leader in the series. Approximately a year after sales of the µPD1708 began, monthly production for the entire series reached the two-million-unit mark, and by the next year that figure had dramatically risen to the three-million-unit level. This was of course thanks to the fact that the performance of the µPD1700 series was highly evaluated by our customers, and soon it was being used not only in luxury cars, but also in a growing number of low-end cars as well.
We went on to branch out from radios and applied the advantages of the µPD1700 series to car audio functions such as cassette deck and CD playback to launch the 17K series and the 178K series, the latter of which is equipped with an 8-bit microcontroller. A general-purpose register architecture (data memory means of a microcontroller) was adopted for both the µPD1700 series and the 17K series. Until then, ordinary microcontroller adopted special-purpose register (accumulator) architecture, for which only certain parts were connected to the operation part. But by adopting the use of a general-purpose register architecture with which any part could be connected to the operation part, many processes could be realized at a low clock frequency and with reduced microcontroller noise. This concept is even used in the latest V850ES/SG3™ and V850ES/SJ3™ 32-bit microcontrollers (Figure 1).
- Product information: Microcomputer 4bit 17K Series (DTS)
- Product information: Microcomputer 8bit 178K Series (DTS)
- Thank you for taking the time to speak with us today.
As you can see, NEC Electronics' microcontrollers for car audio use have evolved from those used for DTS to today's 32-bit microcontrollers equipped with flash memory. Next we will discuss the appeal of our newest product.
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