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Al Williams

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RIP 8 Bit?

April 25, 2010

A good friend of mine - and a great software engineer - decided to work on a hardware project the other day and asked my advice. He apparently had been involved in hardware design early in his career, but has since gone completely over to software. His project - which had something to do with a brother-in-law's business venture - involved sensing a light, delaying, and actuating a signal.My friend wanted to talk about light sensors. But I have one cardinal rule about answering questions. I always ask why you want to know something. Sometimes this seems a little obnoxious, but I've learned my lesson the hard way. Too many non-technical neighbors and relatives have asked me how to increase their PC memory and then after a 30 minute lecture on memory SIMMs they will tell me they really meant disk memory. So my first answer to a question is almost always a return question: ";What is it you actually want to do?";

Once he explained about this light sensor project, I found he wanted to use an LM555 (a venerable and versatile timer IC in case you've lived under a rock or you are under the age of 30) to provide the delay. I'm older than he is, so I certainly have done my share of LM555 projects, but I rapidly tried to talk him out of it.

Looking at my favorite distributor, I see I can get a reel of 2,500 LM555 chips in surface mount for about 43 cents each. Great. But, I need some resistors and capacitors too - quite a few of them actually. That's more cost. And more board space. And the circuit will be completely inflexible. The same distributor will sell me a Microchip PIC10F200 for 37 cents at quantity 100 (and only 56 cents in singles). It has an internal 4MHz oscillator, so I don't need any external parts there. And it has plenty of muscle to read a light sensitive resistor with a single capacitor. Just have the PIC try to charge the capacitor through the resistor and time how long it takes to charge up to a logic ";1"; level).

It actually cost money NOT to put a microprocessor into this circuit! How far away are we from having this same discussion about 8 bit parts? Will they go the way of the LM555? Eventually, I'm sure they will. Even though my mom's web surfing is perfectly handled by an ";old"; single-core Celeron CPU, she'd be unlikely to find a new one to buy and would wind up with a computer much faster than she needs just because a big multicore behemoth would be cheap and easy to find. But I think 8 bit will continue to rule the low end for a little while longer.

Not that bigger chips aren't making a dent. I already turn to some ARM boards I get for about $20 or $30 when I want to do a ";one off."; I've owned PCs that were less capable than these boards and it is just too handy to have that much power for more or less the same price (or less) than I would pay for a similar board with a PIC or AVR on it. If you are doing production quantities, I see that Digikey lists the LPC11111 (although with no stock) for less than $1/each if you are buying at least 100 and pushing towards 80 cents each in large quantities. Still not 37 cents though. But still a far cry from the $3 or $4 some vendors want for their low-end 32-bit CPUs (or, for that matter, the $2 some want for 16-bit parts).

There are applications where price is always king. If larger parts are going to completely displace 8 bit parts, they will have to get cheaper and take care to integrate entire systems. Cost savings evaporate if you have to add oscillators, I/O devices, and other components to flesh out your entire system. This year will see the 8-bit market further shrink, no doubt, but it won't be going away. Not yet, at least. After all, I can still buy 555s.

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