Are you, or would you consider, using a 4-bit microcontroller?

Wednesday, November 24th, 2010 by Robert Cravotta

Jack Ganssle recently asked me about 4-bit microcontrollers. He noted that there are no obvious 4-bit microcontrollers listed in the Embedded Processing Directory – but that is partly because there are so few of them that I “upgraded” them to the 8-bit listing a few years back. In all the years I have been doing the directory, this is the first time someone has asked about the 4-bitters.

I suspect the timing of Jack’s inquiry is related to his recent article “8 bits is dead” where he points out that the predicted death of 8-bit microcontrollers continues to be false – in fact, he predicts “that the golden age of 8 bits has not yet arisen. As prices head to zero, volumes will soar putting today’s numbers to shame.” I agree with him, the small end of the processing spectrum is loaded with potential and excitement, so much so that I started a series on extreme processing thresholds a few months ago to help define where the current state of the art for processing options is so that it is easier to identify when and how it shifts.

The timing of this inquiry also coincides with Axel Streicher’s article asking “Who said 16-bit is dead?” Axel makes a similar observation about 16-bit processors. I would have liked to have seen him point out that 16-bit architectures is also a sweet spot for DSC (digital signal controllers), especially because Freescale was one of the first companies to adopt the DSC naming. A DSC is a hybrid that combines architectural features of a microcontroller and a digital signal processor in a single execution engine.

A comment on Jack’s article suggested that this topic is the result of someone needing a topic for a deadline, but I beg to differ. There are changes in the processing market that constantly raise the question of whether 8- and 16-bitters will finally become extinct. The big change this year was the introduction of the Cortex-M0 – and this provided the impetus for me to revisit this same topic, albeit from a slightly different perspective, earlier this year when I asked “How low can 32 bits processors go?” I offer that a key advantage that smaller processors have over 32-bit processors is that they reach lower cost and energy thresholds several years before 32-bit processors can get there, so the exciting new stuff will be done on the smaller processors long before they are put on a 32-bit processor.

In contrast, the humble 4-bit gets even less to no attention than the 8- and 16-bitters – but the 4-bit microcontroller is not dead either. Epson just posted a new data sheet for a 4-bit microcontroller a few weeks ago (I am working to get them added to the Embedded Processing Directory now). The Epson 4-bitters are legacy devices that are used in time pieces. EM Microelectronics’ EM6607 is a 4-bit microcontroller; I currently have a call to them to clarify its status and find out what types of applications it is used in.You can still find information about Atmel’s MARC4 which the company manages out of their German offices and is not currently investing any new money into.

So to answer Jack’s question – no, 4-bit processors are not dead yet, and they might not die anytime soon. Are any of you using 4-bit processors in any shape or form? Would you consider using them? What types of processing characteristics define a 4-bitter’s sweet spot? Do you know of any other companies offering 4-bit processors or IP?

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3 Responses to “Are you, or would you consider, using a 4-bit microcontroller?”

  1. Rick Hully says:

    The 4-bit is definitely not dead. We have 211 4 bit MCU’s in our Gopher database.

    21 from Atmel
    119 from NEC
    61 from Renesas
    10 from Samsung

  2. Jon Titus says:

    Plenty of uses for 4-bit MCUs in control and monitoring/reporting applications. I suppose they would work well in microwave ovens, refrigerators, and similar devices. Even good for speed control in some AC motors. By the way, in the ’70′s, Motorola offered a 1-bit processor (no, I am not kidding), the MC14500B. The data bus was one bit wide, but the processor used a 4-bit instruction. Do a Google search for the MC14500B data sheet and you’ll get some interesting information.

  3. B.Z. @LI says:

    The one and only time I used a 4-bit machine was when I was asked to take a prototype engine controller using a Signetics 2650 and port it into a COPS400-based controller. I ended up putting the controller software into several different architectures, all of which could do the job. That COPS400 could string 16 nibbles together with BCD arithmetic operations, giving it some computational capability.

    When your entire program runs on-chip and you eliminate the external bus connection, your cost starts dropping and the word length becomes far less relevent. In a high-volume situation, it is the cost of the final custom chip (IP licenses, etc.) that drive the selection. If you are only making a few ten of thousands, then you may want to look at your options. Total cost of operation, from concept to obsolescence.

    4-bit sweet spot? Using BCD comes to mind, making it work for cash transactions with 7-segment displays, RFID transactions with LEDs, any small appliance with a clock/timer, locks with keypads, even personal protection such as detecting when you have been scanned at a close distance.

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