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Clever use of memory devices can really improve your products. Want to extend your workforce's productivity? Reduce Bugs? Meet deadlines? Take Jack's one day Better Firmware Quicker seminar. You’ll discover ways to estimate a schedule accurately, thwart schedule-killing bugs, handle reuse, construct predictable real-time code, higher methods to deal with uniquely embedded problems like reentrancy, heaps, stacks and hardware drivers, and much, rather more. Jack can be presenting this seminar in Chicago (April 23, 2008), Denver (April 25) and Memory Wave London, UK (Might 19). Need to be your company’s embedded guru? Be part of us! More information right here. For hints, tricks and ideas about better methods to build embedded techniques, subscribe to The Embedded Muse, a free biweekly e- newsletter. No advertising, just all the way down to earth embedded speak. Click right here to subscribe. In my October column I wrote about eliminating potentiometers from embedded methods, changing them with smart software to mechanically compute calibration values. Tis a noble endeavor, this elimination of analog elements. However, the place can we store the calibration coefficients?

The great attraction of a potentiometer is its potential to "retailer" an analog worth. As soon as set, it provides a continuing voltage or current whose worth is set by its shaft's position. The worth is remembered even when the system is deprived of energy for long durations. Given that almost all embedded systems don't include classic mass storage units like disks, we'll have to seek out some approach to save our digital pot equal knowledge. Memory Wave Audio is the obvious choice, but information stored in RAM is misplaced when energy is eliminated. AT and 386 class machines all include a "setup" program that determines fundamental working parameters like disk dimension and configuration. This information is normally saved in conventional low power RAM, whose contents are maintained using a easy battery circuit. When power goes down, the battery takes over. Most CMOS static RAMs enter an ultra low energy standby mode when not selected. Normally, they will maintain their contents even at 2 to three volt Vcc levels, so two or three AA cells provides greater than sufficient voltage to maintain the information intact.

There are numerous battery-backed up methods around. Quite a number of undergo from poor design which exhibits itself by occasional information dropouts. That is unforgivable: no one, but no person, messes with my information! When my three 12 months previous destroyed the dishwasher, I might understand. When he broke the VCR, I figured that, effectively, he has to learn even at the expense of some electronics. However then he innocently disassembled a floppy disk - that was hard to forgive! Most designs isolate the RAM's most important energy provide from the battery circuit utilizing a diode or equivalent transistor circuit. With out the diode, when energy is down the battery will likely be referred to as on to run your complete computer. Silicon diodes have a junction drop equal to around .7 volts. A 5.0 volt provide might be only 4.3 or so when measured on the diode's cathode. While more than enough to retain information, it's lower than needed to run the RAM during regular operation.

Anything lower than 4.Seventy five volts is just too low. Sadly, most RAMs will roughly run with Vcc under specification, so these circuits typically appear to work; usually, simply until 500 manufacturing boards are built. The answer is to use a Shottkey diode. Though slightly costlier, it only loses .1 volt in the junction. It's a easy, well known resolution, however most of the methods we see still use silicon diodes. The other essential ingredient of profitable battery backup is a circuit to shut down the processor as soon as energy goes below 4.75 volts. A CPU will run wild with low power. Sooner or later, as the facility slowly decays it can execute an instruction that wipes out your rigorously preserved RAM data. In actual fact, battery backup just isn't always an excellent answer. The batteries are physically huge, laborious to mount on a circuit board, and should be changed each so often.