NetSilicon's 32-bit MCU takes aim at 16-bit slots -

NetSilicon’s 32-bit MCU takes aim at 16-bit slots

BOSTON — NetSilicon Inc. hopes to steal microcontroller slots from 16-bit devices with a stripped-down 32-bit ARM7TDMI-based MCU tailored for low cost. The controller, designated the NS7520 and slated to debut here Monday (Nov. 18) at the Embedded Systems Conference, is the first in a family of 33- to 55-MHz devices that will be priced at less than $10 each in volume.

Selling for $7.95 apiece in 10,000-unit quantities, the NS7520 targets the core of the 16-bit microcontroller's domain: hard-real-time deterministic control applications in industrial environments, automotive engines and building automation. The 177-pin device, in a ball-grid array package, is sampling now and is expected to ship in volume in January.

“Many developers in hard-core control applications have begun to ask for more capabilities, more memory and more Internet-centric functionality than they are able to get in 16-bit configurations,” said Tim Counihan, vice president of marketing at the Waltham, Mass.-based company.

The move comes as 16-bit vendors look to flesh out TCP/IP connectivity and add management functions such as the Simple Network Management Protocol, to become more full-fledged members of the fraternity of Internet-centric device providers.

The problem for 8/16-bit controller makers is that because of the MCUs' limited processor capabilities and minuscule memory address capacity, TCP/IP additions have by necessity been limited to subsets of the full Internet protocols. Some manufacturers borrowed a strategy used by 16-bit MCU makers to take market share from 8-bit vendors: put a wider byte-size architecture inside an 8-bit device, but keep the interface fully 8 bit.

To protect their turf from 32-bit incursions, 16-bit MCU vendors such as Microchip Technology Inc. have moved to internal architectures of 20- and 24-bit word widths to allow faster operation at no additional cost. Many of Motorola's nominally 16-bit MCUs have an internal 32-bit architecture. Others, such as Ubicom Inc., use advanced processing to achieve clocks rates in excess of 100 MHz and tap on-chip data and program storage to perform many control and network functions in software rather than hardware.

Most 32-bit controller vendors, including Motorola and about half a dozen licensees of ARM Ltd.'s real-time and deterministically optimized ARM7TDM1 core, have a different focus. In addition to many nonreal-time deterministic applications in a range of PDAs and other small-footprint systems, they have targeted environments (such as home networking) and applications (such as network bridges and gateways) that, at the lower levels of the network protocols, must operate in a real-time, deterministic manner.

But few 32-bit vendors have gone after the core of the 16-bit MCU market — not even Ubicom, which recently revealed the architectural details of a 32-bit MCU of original design.

Meanwhile, Philips' use of the ARM7TDMI in its new family of 32-bit devices has provided a migration path for many controller peripheral functions and software expertise to real-time 32-bit control applications in the lower levels of the network protocol stacks. The Philips devices are scheduled to go into production later this year.

Bill Peisel, chief technical officer at NetSilicon, believes it is time to go after the core of the 16-bit business, using the ARM7TDMI as the vehicle. On the one hand, he said, ARM has minimized or removed architectural features such as on-chip memory management and the data and program caches. While useful in a wide range of data-processing applications, such features get in the way of deterministic control functions. On the other hand, he said, ARM was smart enough to incorporate a vectored interrupt controller block into the core.

Reducing die size

The trick, said Peisel, is to retain as much of this control functionality as possible while reducing the die size enough to match 16-bit microcontrollers in price.

The first step was to include only that functionality necessary for the majority of real-time microcontroller functions. Much of what was left on the chip is familiar to any engineer versed in 16-bit designs, Peisel said.

To reduce the die size sufficiently to match 16-bit MCU pricing models, the company also shifted to a new fabrication partner and a new process (Toshiba and its 0.18-micron CMOS process, vs. Atmel's 0.25-micron CMOS). That shift, in combination with the reduction in architectural complexity, led NetSilicon to reduce the die area 30 to 40 percent, sufficient to fit into a 177-pin BGA, vs. the previous, 208-pin BGA.

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