Considerations for 4-bit processing

Friday, December 10th, 2010 by Robert Cravotta

I recently posed a question of the week about who is using 4-bit processors and for what types of systems. At the same time, I contacted some of the companies that still offer 4-bit processors. In addition to the three companies that I identified as still offering 4-bit processors (Atmel, EM Microelectronics, and Epson), a few readers mentioned parts from NEC Electronics, Renesas, Samsung, and National. NEC Electronics and Renesas merged and Renesas Electronics America now sells the combined set of those company’s processor offerings.

These companies do not sell their 4-bit processors to the public developer community in the same way that 8-, 16-, and 32-bit processors are. Atmel and Epson told me their 4-bit lines support legacy systems. The Epson lines support most notably timepiece designs. I was able to speak with EM Microelectronics at length about their 4-bit processors and gained the following insights.

Programming 4-bit processors is performed in assembly language only. In fact, the development tools cost in the range of $10,000 and the company loans the tools to their developer clients rather than sell them. 4-bit processors are made for dedicated high volume products – such as the Gillette Fusion ProGlide. The 4-bit processors from EM Microelectronics are available only as ROM-based devices, and this somewhat limits the number of designs the company will support because the process to verify the mask sets is labor intensive. The company finds the designers that can make use of these processors – not the other way around. The company approaches a developer and works to demonstrate how the 4-bit device can provide differentiation to the developer’s design and end product.

The sweet spot for 4-bit processor designs are single battery applications that have a 10 year lifespan and where the device is active perhaps 1% of that time and in standby the other 99%. An interesting differentiator for 4-bit processors is that they can operate at 0.6V. This is a substantial advantage over the lowest power 8-bit processors which are still fighting over the 0.9 to 1.8V space. Also, 4-bit processors have been supporting energy harvesting designs since 1990 whereas 8- and 16-bit processor vendors are only within the last year or so beginning to offer development and demonstration kits for energy harvesting. These last two revelations strengthen my claim in “How low can 32-bit processors go” that smaller sized processors will reach lower price and energy thresholds years before the larger processors can feasibly support those same thresholds – and that time advantage is huge.

I speculate that there may be other 4-bit designs out there, but the people using them do not want anyone else to know about them. Think about it, would you want your competitor to know you were able to simplify the problem set to fit on such a small device? Let them think you are using a larger, more expensive (cost and energy) device and wonder how you are doing it.

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