The main appeal of the serial peripheral interface (SPI) flash lies in its reduced cost and power consumption. On the other hand, parallel interface NOR flash delivers high performance and security features, which outplay cost and power concerns in embedded applications.

"System designers prefer to use SPI rather than parallel flash, especially in consumer applications," Brady Wang, principal research analyst at Gartner, told EE Times in an email interview. "The serial interface offers several benefits over the parallel interface, including lower overall systems costs, smaller and simpler printed circuit boards, and lower power consumption." As a result, the share of serial memory revenue increased from 19.8 per cent in 2010 to 46.5 per cent in 2013, and it is expected to hit 64.7 per cent in 2017, and almost all mid- and low-density NOR flash are serial in 2014.

Though NOR flash, including parallel NOR, continues to have specific application uses where speed and performance are a factor, an IHS report issued in February said it continues to struggle, especially in relation to NAND flash. The NOR market has been steadily declining since 2007.

Wang said that, even though the applications for mid- and high-density parallel NOR flash are limited, they do enjoy better margins than others. Since parallel can provide fast reading speed, it could be used in performance-driven applications, such as automotive displays, wired devices such as set-top boxes, and industrial roles.

In 2013, Wang said, the major parallel NOR flash vendors were Micron with 34.8 per cent of the market, Spansion with 32.1 per cent, Macronix with 8 per cent, and Microchip Technology with 4.1 per cent.

This month, Microchip introduced its SST38VF6401B parallel flash memory device, which offers high performance with flexible read and write options, including random read access time of 70ns and page read access time of 25ns. Randy Drwinga, vice president of Microchip's memory products division, said the device can be used in a wide variety of applications, including those in the consumer, automotive, and industrial markets.

The SST38VF6401B is designed to be highly configurable by the customer, especially for devices that are graphics intensive, such as set-top boxes and audio, video, and infotainment products for automobiles. Drwinga said a frequent customer requirement is the ability to program multiple languages easily for use cases such as digital signage.

Another important feature is security at different layers, not just to prevent access, he said, but to ensure data can't be corrupted. Devices such as integrated infotainment systems in cars, set-top boxes, or even programmable coffee makers won't start if core data is accidently changed—they end up displaying their own blue screen of death.

Hiro Ino, senior director of product line management for Spansion's flash memory group, said that level of reliability is crucial. "If the system gets corrupted, it's a catastrophic failure. The data has to be resilient and robust."

Speed is also crucial, especially in the growing automotive segment; drivers expect their digital dashboards to start up quickly. These displays used to be mechanical, but now they are extremely graphics intensive. "When you turn the ignition on, the first thing the driver wants is for the instrument cluster to pop up right away," he said. A serial device would take about 15 seconds to start up, while a parallel device would take roughly 10 seconds.

In February, Spansion took its NOR flash offering to another level with the introduction of its HyperFlash line of NOR memory devices, which feature read throughput of up to 333MB/s. Ino said this is more than five times faster than ordinary Quad SPI flash with one-third the number of pins of parallel NOR flash. Bringing it back to the car analogy, HyperFlash allows vehicle instrumentation to come online in approximately three seconds.

Durability is also important, he said. In a car and other equipment, these devices have to withstand a wide range of temperatures. In addition, once the memory is in the equipment, customers do not want to have access physically the device's guts (including the memory) for long periods of time. This is particularly true for field applications such as wireless bay stations or digital signage.

"If they aren't reliable enough, servicemen will have to go in and fix it," Ino said. "The maintenance costs are very expensive."

By: DocMemory
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